Solar cell and method for manufacturing the same

ABSTRACT

A solar cell can include a silicon semiconductor substrate; an oxide layer on a first surface of the silicon semiconductor substrate; a polysilicon layer on the oxide layer; a diffusion region at a second surface of the silicon semiconductor substrate; a dielectric film on the polysilicon layer; a first electrode connected to the polysilicon layer through the dielectric film; a passivation film on the diffusion region; and a second electrode connected to the diffusion region through the passivation film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/995,701 filed on Jun. 1, 2018, which is a Continuation of U.S. patentapplication Ser. No. 15/643,180 filed on Jul. 6, 2017 (now U.S. Pat. No.10,014,419 issued on Jul. 3, 2018), which is a Continuation of U.S.patent application Ser. No. 14/953,264 filed on Nov. 27, 2015 (now U.S.Pat. No. 9,722,104 issued on Aug. 1, 2017), which claims priority to andthe benefit of Korean Patent Application No. 10-2014-0168624 filed inthe Korean Intellectual Property Office on Nov. 28, 2014, and KoreanPatent Application No. 10-2015-0122846 filed in the Korean IntellectualProperty Office on Aug. 31, 2015, the entire contents of all theseapplications are incorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the present invention relate to a solar cell and a methodfor manufacturing the same.

Discussion of the Related Art

Recently, as the exhaustion of existing energy resources, such aspetroleum and coal, is expected, there is a growing interest inalternative energy sources which will replace the existing energyresources. A solar cell as the alternative energy sources generateselectric power from solar energy and has been in the spotlight becausethe solar cell uses energy resources that are abundant and the solarcell has no problem from an environmental pollution point of view.

A solar cell includes substrates made of semiconductors having differentconductive types, such as a p type and an n type, a second conductivetype semiconductor region (or emitter layer), and electrodesrespectively connected to the substrates and the second conductive typesemiconductor region. A p-n junction is formed at the interface of thesubstrate and the second conductive type semiconductor region.

When light is incident on such a solar cell, a plurality ofelectron-hole pairs are generated from the semiconductors. The generatedelectron-hole pairs are separated into electrons and holes. Theseparated electrons and holes move toward the n type semiconductor andthe p type semiconductor, for example, toward the second conductive typesemiconductor region and the substrate, respectively, and are collectedby the electrodes electrically connected to the substrates and thesecond conductive type semiconductor region. The electrodes areconnected by lines, thereby obtaining power.

SUMMARY OF THE INVENTION

A solar cell according to an example of the present invention includes asemiconductor substrate, a tunnel layer on the first surface of thesemiconductor substrate, a first conductive type semiconductor region onthe tunnel layer and configured to include impurities of a firstconductive type, a second conductive type semiconductor region on asecond surface which is the opposite surface of the semiconductorsubstrate and configured to include impurities of a second conductivetype opposite the first conductive type, a first passivation film on thefirst conductive type semiconductor region, a first electrode formed onthe first passivation film and connected to the first conductive typesemiconductor region through an opening portion formed in the firstpassivation film, a second passivation film on the second conductivetype semiconductor region, and a second electrode formed on the secondpassivation film and connected to the second conductive typesemiconductor region through an opening portion formed in the secondpassivation film.

In this instance, the first electrode may include a plurality of firstfinger electrodes spaced apart from each other and extended in parallelin a first direction, and the second electrode may include a pluralityof second finger electrodes spaced apart from each other and extended inparallel in the first direction.

Furthermore, the first electrode may further include a first bus barconfigured to interconnect the plurality of first finger electrodes, andthe second electrode may further include a second bus bar configured tointerconnect the plurality of second finger electrodes.

In this instance, the first conductive type semiconductor region may bemade of a polycrystalline silicon material, and the second conductivetype semiconductor region may be made of a single crystal siliconmaterial.

Furthermore, an isolation portion for preventing a contact between thefirst conductive type semiconductor region and the second conductivetype semiconductor region may be formed on any one of the first surface,side, and second surface of the semiconductor substrate.

For example, the isolation portion may exclude the tunnel layer and thefirst conductive type semiconductor region, and may be in the edgeportion of any one of the first surface, side, and second surface of thesemiconductor substrate. The first passivation film may cover any one ofthe first surface, side, and second surface of the semiconductorsubstrate along with the isolation portion.

In this instance, the width of the isolation portion may be 1 nm to 1mm. The thickness of the edge region in the first conductive typesemiconductor region may be progressively decreased toward the isolationportion.

Furthermore, the first passivation film may include a side portionextending up the side of the semiconductor substrate.

Moreover, the second passivation film may include a side portion formedon the side surface of the semiconductor substrate. The side portion ofthe first passivation film on the side of the semiconductor substratemay be on the side portion of the second passivation film.

Furthermore, a first boundary surface in which the first conductive typesemiconductor region and the first electrode come into contact with eachother may be closer to the semiconductor substrate than a secondboundary surface in which the first conductive type semiconductor regionand the first passivation film come into contact with each other.

In this instance, a plurality of metal crystals extracted from the firstelectrode may be in an electrode forming region which belongs to thefirst conductive type semiconductor region and in which the firstelectrode may be formed. That is, the metal crystals may not be in anon-forming region which belongs to the first conductive typesemiconductor region and in which the first electrode may not be formed.Furthermore, the metal crystals may not be in the tunnel layer.

The plurality of metal crystals may be in direct contact with the firstelectrode or may be spaced apart from the first electrode.

In this instance, all of the plurality of first finger electrodes andthe first bus bar may be connected to the first conductive typesemiconductor region through the first passivation film.

In this instance, all of the plurality of first finger electrodes andthe first bus bar may have a single layer or double layer structure. Insome embodiments, the plurality of first finger electrodes may have asingle layer structure, and the first bus bar may have a double layerstructure.

In this instance, the plurality of metal crystals may be in a regionwhich belongs to the first conductive type semiconductor region and inwhich the plurality of first finger electrodes is formed and a regionwhich belongs to the first conductive type semiconductor region and inwhich the first bus bar is formed.

In some embodiments, the plurality of first finger electrodes may beconnected to the first conductive type semiconductor region through thefirst passivation film. The first bus bar may be configured to notpenetrate the first passivation film and may be formed on the backsurface of the first passivation film.

In this instance, the plurality of metal crystals may be in a regionwhich belongs to the first conductive type semiconductor region and inwhich the first finger electrodes are formed. The plurality of metalcrystals may not be in a region which belongs to the first conductivetype semiconductor region and in which the first bus bar is formed.

In this instance, the plurality of first finger electrodes and the firstbus bar may have different compositions. For example, a content of afrit glass per unit volume which is included in the plurality of firstfinger electrodes may be greater than a content of a frit glass per unitvolume which is included in the first bus bar.

Furthermore, a content of a frit glass per unit volume which is includedin the plurality of first finger electrodes may be identical with acontent of a frit glass per unit volume which is included in the firstbus bar.

Furthermore, content of a metal material per unit volume which isincluded in the plurality of first finger electrodes may be greater thancontent of a metal material per unit volume which is included in thefirst bus bar.

Furthermore, a method for manufacturing a solar cell according to anexample of the present invention includes a tunnel layer formingoperation of forming a tunnel layer on the first surface of asemiconductor substrate, an intrinsic semiconductor layer formingoperation of forming an intrinsic semiconductor layer on the tunnellayer formed on the first surface of the semiconductor substrate, afirst conductive type semiconductor region forming operation of forminga first conductive type semiconductor region by doping impurities of afirst conductive type into the intrinsic semiconductor layer formed onthe first surface of the semiconductor substrate, a second conductivetype semiconductor region forming operation of forming a secondconductive type semiconductor region by doping impurities of a secondconductive type into the second surface of the semiconductor substrate,a first passivation film forming operation of forming a firstpassivation film on the first conductive type semiconductor region, andan electrode forming operation of forming a first electrode connected tothe first conductive type semiconductor region and a second electrodeconnected to the second conductive type semiconductor region.

In this instance, the method may further include the operation offorming an opening portion in the first passivation film after the firstpassivation film forming operation.

The operation of forming the opening portion in the first passivationfilm may be performed by thermal treatment in the electrode formingoperation.

The electrode forming operation may include a first electrode formingoperation of forming the first electrode. The first electrode formingoperation may include printing a paste for first finger electrodes forforming the first finger electrodes and a paste for a first bus bar forforming the first bus bar on the first passivation film and performingthermal treatment on the pastes. During such a thermal treatmentprocess, the paste for the first finger electrodes and the paste for thefirst bus bar may perforate the first passivation film and may beconnected to the first conductive type semiconductor region. In thisinstance, the opening portion may be formed in the first passivationfilm.

In the first electrode forming operation, the highest temperature forthe thermal treatment may be between 795° C. to 870° C.

In the first electrode forming operation, the paste for the first fingerelectrodes and the paste for the first bus bar may be printed through asingle process. In this instance, a material included in the paste forthe first finger electrodes may be identical with a material included inthe paste for the first bus bar.

Furthermore, in some embodiments, in the first electrode formingoperation, the paste for the first finger electrodes and the paste forthe first bus bar may be printed using separate printing processes. Inthis instance, a material included in the paste for the first fingerelectrodes and a material included in the paste for the first bus barmay be different.

Furthermore, the tunnel layer forming operation may include forming thetunnel layer on the first and second surfaces of the semiconductorsubstrate. The intrinsic semiconductor layer forming operation mayinclude forming the intrinsic semiconductor layer on the tunnel layersformed on the first and second surfaces of the semiconductor substrate.The method may further include a removing operation of removing thetunnel layer and the intrinsic semiconductor layer or the firstconductive type semiconductor region placed at least on the secondsurface of the semiconductor substrate prior to the second conductivetype semiconductor region forming operation after the first conductivetype semiconductor region forming operation.

The removing operation may include forming an isolation portion byremoving the tunnel layer placed on one side of the semiconductorsubstrate and an edge portion of the first conductive type semiconductorregion. The first passivation film may cover the first surface of thesemiconductor substrate along with the isolation portion.

More specifically, the removing operation may include forming a masklayer having a smaller area than the semiconductor substrate on thefirst conductive type semiconductor region on the other side of thesemiconductor substrate, etching the first conductive type semiconductorregion and the tunnel layer placed in a portion in which the mask layerhas not been formed, and removing the mask layer.

Furthermore, the method may further include forming a second passivationfilm covering the second conductive type semiconductor region betweenthe operation of forming the second conductive type semiconductor regionand the operation of forming the first passivation film. The secondpassivation film may be placed on the side of the semiconductorsubstrate, and the first passivation film may be placed on the secondpassivation film.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention.

FIGS. 1 to 3 are diagrams illustrating a solar cell according to a firstembodiment of the present invention;

FIG. 4 is a cross-sectional view of a solar cell for illustrating amodified example of the first embodiment of the present invention;

FIGS. 5 to 7 depict a solar cell according to a second embodiment of thepresent invention;

FIG. 8 depicts a comparison example different from the second embodimentof the present invention;

FIG. 9 is a diagram illustrating a solar cell according to a thirdembodiment of the present invention;

FIG. 10 is a comparison example photograph of the degree of thedeterioration of a semiconductor substrate 100 according to firingtemperatures in a thermal treatment process, which was taken throughphoto luminescence (PL), if the material of a paste for first bus bar isthe same as the material of a paste for first finger electrodes;

FIG. 11 is photograph of the degree of the deterioration of thesemiconductor substrate according to firing temperatures in a thermaltreatment process, which was taken through photo luminescence (PL), ifthe material of the paste for the first bus bar is different from thematerial of the paste for the first finger electrodes in accordance withthe third embodiment of the present invention;

FIG. 12 is a flowchart illustrating an example of a method formanufacturing a solar cell according to a first embodiment of thepresent invention;

FIGS. 13A to 13J are cross-sectional views of the method formanufacturing a solar cell according to the flowchart of FIG. 12 ;

FIG. 14 is a diagram illustrating a modified example of the method formanufacturing a solar cell according to the first embodiment;

FIG. 15 is a diagram illustrating another modified example of the methodfor manufacturing a solar cell according to the first embodiment;

FIG. 16 is a flowchart illustrating an example of a method formanufacturing a solar cell according to a second embodiment of thepresent invention; and

FIG. 17 is a flowchart illustrating an example of a method formanufacturing a solar cell according to a third embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention are described more fullyhereinafter with reference to the accompanying drawings. As thoseskilled in the art would realize, the described embodiments may bemodified in various different ways, all without departing from thespirit or scope of the present invention. In order to clarify adescription of the present invention, a description of parts not relatedto the description is omitted, and the same reference numbers are usedthroughout the specification to refer to the same or like parts.

In the drawings, the thickness of layers and an area has been enlargedfor better understanding and ease of description. When it is describedthat a part, such as a layer, film, area, or substrate, is “over” or“on” another part, the part may be “directly” on another part or a thirdpart may be present between the two parts. In contrast, when it isdescribed that a part is “directly on” another part, it means that athird part is not present between the two parts. Furthermore, when it isdescribed that a part is “generally” formed on another part, it meansthe part is not formed on the entire surface (or front surface) ofanother part and is also not formed in part of the edge of the entiresurface.

Furthermore, expressions, such as “the first” and “the second”, are usedto distinguish one part from the other part, and the present inventionis not limited thereto.

Furthermore, a “front surface” may be one surface of a semiconductorsubstrate on which direct light is incident, and a “back surface” may bethe opposite surface of the semiconductor substrate on which directlight is not incident or on which reflected light other than directlight may be incident.

Furthermore, if two values are the same, it means that the two valuesare the same within an error range of 10% or less.

Solar cells and methods for manufacturing the same according toembodiments of the present invention are described in detail below.

FIGS. 1 to 3 are diagrams illustrating a solar cell according to a firstembodiment of the present invention.

FIG. 1 is a partial perspective view of the solar cell according to thefirst embodiment of the present invention, FIG. 2 is the entirecross-sectional view of the solar cell according to the first embodimentof the present invention, and FIG. 3 is the entire plan view of the backsurface of the solar cell according to the first embodiment of thepresent invention.

Furthermore, FIG. 4 is a cross-sectional view of a solar cell forillustrating a modified example of the first embodiment of the presentinvention.

As shown in FIG. 1 , an example of a solar cell according to anembodiment of the present invention includes a semiconductor substrate100, a second conductive type semiconductor region 120, ananti-reflection layer 130, a tunnel layer 160, a first conductive typesemiconductor region 170, a first passivation film 190A, a secondpassivation film 190B, a second electrode 140, and a first electrode150.

In FIG. 1 , the solar cell according to an embodiment of the presentinvention has been illustrated as including the anti-reflection layer130 and the second passivation film 190B, but the anti-reflection layer130 and the second passivation film 190B may be omitted in someembodiments. However, an example in which the anti-reflection layer 130and the second passivation film 190B are included in the solar cell isdescribed below because better efficiency is obtained if theanti-reflection layer 130 and the second passivation film 190B areincluded from a viewpoint of efficiency of the solar cell.

The semiconductor substrate 100 may be made of a crystallinesemiconductor including a single semiconductor material (e.g., a group 4element). For example, the semiconductor substrate 100 may be made of asingle crystal or polycrystalline semiconductor (e.g., single crystal orpolycrystalline silicon). In particular, the semiconductor substrate 100may be made of a single crystal semiconductor (e.g., a single crystalsemiconductor wafer, more specifically, a single crystal silicon wafer).

If the semiconductor substrate 100 is made of a single crystalsemiconductor (e.g., single crystal silicon) as described above, thesolar cell is based on the semiconductor substrate 100 made of a singlecrystal semiconductor having less defects because it has highcrystallizability. Accordingly, the solar cell can have excellentelectrical characteristics. In embodiments of the invention,crystallizability may refer to a degree to which a material may becrystallize or crystallizable, for example.

Furthermore, the front surface and/or back surface of the semiconductorsubstrate 100 may be textured and may have concave-convex portions. Forexample, an external surface of the concave-convex portions may beformed of the (111) face of the semiconductor substrate 100 and may havea pyramid shape having an irregular size.

If the concave-convex portions are formed in the front surface of thesemiconductor substrate 100 by texturing as described above and thus thesurface roughness of the front surface is increased, the reflectance oflight incident through the front surface of the semiconductor substrate100 can be reduced.

Accordingly, an optical loss can be minimized because the amount oflight which reaches a pn junction formed by a base region 110 and thefirst or second conductive type semiconductor region 170 or 120 isincreased. In the present embodiment, the concave-convex portions havebeen illustrated as being formed in the front and back surfaces of thesemiconductor substrate 100, thereby effectively preventing thereflection of light incident through both surfaces.

However, the present invention is not limited to the example.Accordingly, as shown in FIG. 4 , the concave-convex portions may beformed only in the front surface of the semiconductor substrate 100, andconcave-convex portions may not be formed in the back surface of thesemiconductor substrate 100.

In this instance, the back surface of the semiconductor substrate 100 inwhich the tunnel layer 160 is formed may be formed to have smallersurface roughness than the front surface thereof so that the tunnellayer 160 is formed more stably and uniformly. Alternatively, thepresent invention may be modified in various ways, for example,concave-convex portions may not be formed in the front and back surfacesof the semiconductor substrate 100.

Referring back to FIG. 2 , in the present embodiment, the semiconductorsubstrate 100 may include the base region 110 doped with impurities of afirst or second conductive type at a low doping concentration andconfigured to have the first or second conductive type.

In this instance, the base region 110 of the semiconductor substrate 100may have a lower doping concentration, higher resistance, or lowercarrier concentration than one of the first and second conductive typesemiconductor regions 170 and 120, which has the same conductive type asthe base region 110.

The first conductive type semiconductor region 170 having the firstconductive type may be placed on one surface (e.g., the back surface) ofthe semiconductor substrate 100. For example, the tunnel layer 160 maybe formed on the semiconductor substrate 100, and the first conductivetype semiconductor region 170 may be formed on the tunnel layer 160.

In this instance, the tunnel layer 160 may be disposed on the backsurface of the semiconductor substrate 100 and may have a direct contactwith the semiconductor substrate 100.

Such a tunnel layer 160 may be generally formed in portions other thanan isolation portion I in the back surface of the semiconductorsubstrate 100. In this instance, “generally formed” may include“generally formed closely” and “some areas are not inevitably formed.”Accordingly, the tunnel layer 160 can be easily formed because aseparate patterning process is not required. However, the presentinvention is not limited to such an example.

Such a tunnel layer 160 may generate a tunneling effect. Morespecifically, the tunnel layer 160 may function as a kind of barrier forelectrons and holes.

That is, the tunnel layer 160 may not transmit minority carriers. Afterthe minority carriers are accumulated in a portion neighboring thetunnel layer 160, only majority carriers having energy of a specificlevel or higher may pass through the tunnel layer 160. The majoritycarriers having energy of a specific level or higher may easily passthrough the tunnel layer 160 by a tunneling effect.

Furthermore, the tunnel layer 160 may also function as a diffusionbarrier for preventing the dopant of the first conductive typesemiconductor region 170 from being diffused into the semiconductorsubstrate 100. The tunnel layer 160 may include various materialsthrough which majority carriers can be tunneled. For example, the tunnellayer 160 may include oxides, nitrides, a semiconductor, and aconductive polymer.

In particular, the tunnel layer 160 may be formed of a silicon oxide(SiOx) layer including silicon oxide. The reason for this is that thesilicon oxide layer has an excellent passivation characteristic andcarriers can easily tunnel through the silicon oxide layer.

In some embodiments, the tunnel layer 160 may be made of a dielectricmaterial including SiCx having strong durability even in a hightemperature process or may be made of SiNx, hydrogenated SiNx, AlOx,SiON, or hydrogenated SiON.

Furthermore, in order to sufficiently implement the tunneling effect,the thickness of the tunnel layer 160 may be smaller than the thicknessof each of the first and the second passivation films 190A and 190B andthe first and the second conductive type semiconductor regions 170 and120.

For example, the thickness of the tunnel layer 160 may be 0.5 nm 2.5 nm.In this instance, the tunnel layer 160 may be formed by an oxidationprocess, an LPCVD process, or a PECVD deposition process, for example.

The thickness of the tunnel layer 160 is limited to the range of 0.5 nm2.5 nm in order to implement the tunneling effect. The range of 0.5 nm2.5 nm may be slightly exceeded. In this instance, however, thetunneling effect may be reduced.

More specifically, the tunnel layer 160 is formed to have the thicknessof 0.5 nm or higher because it is practically very difficult to form thetunnel layer 160 having a thickness of less than 0.5 nm. Furthermore,the tunnel layer 160 is formed to have the thickness of 2.5 nm or lessbecause the tunneling effect is meager if the thickness exceeds 2.5 nm.

The first conductive type semiconductor region 170 may be placed on theback surface of the semiconductor substrate 100, may include impuritiesof the first conductive type having a higher concentration than theimpurities of the first conductive type included in the semiconductorsubstrate 100, and may include a polycrystalline silicon material.

That is, the first conductive type semiconductor region 170 may beformed on the back surface of the tunnel layer 160 formed on the backsurface of the semiconductor substrate 100 and may be isolated from thesemiconductor substrate 100, as shown in FIG. 1 .

The first conductive type semiconductor region 170 may be brought intocontact with and formed on the tunnel layer 160, thereby simplifying thestructure of the solar cell and maximizing the tunneling effect of thetunnel layer 160.

If the first conductive type semiconductor region 170 is not formedwithin the semiconductor substrate 100, the first conductive typesemiconductor region 170 is formed on the back surface of thesemiconductor substrate 100, but spaced apart from the semiconductorsubstrate 100 as shown in FIGS. 1 and 2 , and the first conductive typesemiconductor region 170 includes a polycrystalline silicon materialformed on the back surface of the tunnel layer 160, the open voltage Vocof the solar cell can be further improved.

Furthermore, the first conductive type semiconductor region 170 is notformed within the semiconductor substrate 100, but is formed outside thesemiconductor substrate 100. Accordingly, the characteristics of thesemiconductor substrate 100 can be prevented from being deterioratedbecause thermal damage to the semiconductor substrate 100 is minimizedin the process of forming the first conductive type semiconductor region170 from a viewpoint of a manufacturing process. Accordingly, anembodiment of the present invention can further improve efficiency ofthe solar cell.

The thickness of the first conductive type semiconductor region 170 maybe 50 nm 500 nm.

The first conductive type semiconductor region 170 may include the samesemiconductor material (more specifically, a silicon semiconductormaterial) as the semiconductor substrate 100. Accordingly, a differencebetween the characteristics of the second conductive type semiconductorregion 120 and the semiconductor substrate 100 can be minimized becausethe second conductive type semiconductor region 120 has similarcharacteristics as the semiconductor substrate 100.

In this instance, since the first conductive type semiconductor region170 is formed on the semiconductor substrate 100 separately from thesemiconductor substrate 100, the first conductive type semiconductorregion 170 may have a crystal structure different from the crystalstructure of the semiconductor substrate 100 so that it is easily formedon the semiconductor substrate 100.

For example, the first conductive type semiconductor region 170 may beformed by doping impurities of the first conductive type into anamorphous silicon material, a fine crystal silicon material, or apolycrystalline silicon material which may be easily manufactured usingvarious methods, such as deposition.

In particular, if the first conductive type semiconductor region 170includes a polycrystalline silicon material, carriers can smoothly movebecause the first conductive type semiconductor region 170 has excellentelectrical conductivity and the tunneling of carriers can be smoothlygenerated in the tunnel layer 160 made of oxide.

The second conductive type semiconductor region 120 is placed on theopposite surface of the semiconductor substrate 100, for example, on thefront surface of the semiconductor substrate 100 on which light isincident. The second conductive type semiconductor region 120 mayinclude impurities of the second conductive type which is opposite theconductive type of the semiconductor substrate 100, for example, aconductive type of an n type.

For example, in the present embodiment, the second conductive typesemiconductor region 120 may be formed into a doping region formed bydoping impurities of the second conductive type into part of thesemiconductor substrate 100.

For example, the second conductive type semiconductor region 120 may beformed by diffusing the impurities of the second conductive type intothe front surface of the semiconductor substrate 100. In this instance,the second conductive type semiconductor region 120 may be made of thesame silicon material as the semiconductor substrate 100.

For example, if the semiconductor substrate 100 is formed of a wafermade of a polycrystalline silicon material, the second conductive typesemiconductor region 120 may also be made of a polycrystalline siliconmaterial. Furthermore, the second conductive type semiconductor region120 in which the semiconductor substrate 100 is formed of a wafer madeof a single crystal silicon material may also be made of a singlecrystal silicon material.

The base region 110 and the second conductive type semiconductor region120 may have the same crystal structure and semiconductor material asthe semiconductor substrate 100, but may have different conductive typesor different doping concentrations.

More specifically, if the base region 110 has the first conductive type,the base region 110 and the second conductive type semiconductor region120 may have different conductive types. If the base region 110 has thesecond conductive type, the second conductive type semiconductor region120 may have a higher doping concentration than the base region 110.

If the base region 110 has the first conductive type, the firstconductive type semiconductor region 170 having the first conductivetype has the same conductive type as the semiconductor substrate 100 andmay form a back surface field (BSF) region which has a higher dopingconcentration than the semiconductor substrate 100 and forms a BSF. Thesecond conductive type semiconductor region 120 having the secondconductive type has a conductive type different from that of the baseregion 110 and may form an emitter region forming a pn junction alongwith the base region 110.

Accordingly, the second conductive type semiconductor region 120 formingthe emitter region is placed on the front surface side of thesemiconductor substrate 100, thereby being capable of minimizing thepath of light regioned with the pn junction.

However, the present invention is not limited to the example. Forexample, if the base region 110 has the second conductive type, thefirst conductive type semiconductor region 170 forms the emitter region,and the second conductive type semiconductor region 120 has the sameconductive type as the semiconductor substrate 100 and may form a frontsurface field (FSF) region which has a higher doping concentration thanthe semiconductor substrate 100 and forms a FSF.

A p type dopant used as the impurities of the first or second conductivetype may include group 3 elements, such as boron (B), aluminum (Al),gallium (Ga), and indium (In). An n type dopant used as the impuritiesof the first or second conductive type may include group 5 elements,such as phosphorous (P), arsenic (As), bismuth (Bi), and antimony (Sb).However, the present invention is not limited to the examples, andvarious dopants may be used as the impurities of the first or secondconductive type.

In the present embodiment, the first conductive type semiconductorregion 170 formed separately from the semiconductor substrate 100 may beplaced on the back surface side of the semiconductor substrate 100, andthe second conductive type semiconductor region 120 forming part of thesemiconductor substrate 100 may be placed on the front surface side ofthe semiconductor substrate 100.

If the first conductive type semiconductor region 170 having a crystalstructure different from that of the semiconductor substrate 100 isplaced on the front surface side of the semiconductor substrate 100, theamount of light reaching the pn junction may be reduced because theabsorption of light in the first conductive type semiconductor region170 is increased. Accordingly, the first conductive type semiconductorregion 170 may be placed on the back surface side of the semiconductorsubstrate 100, but the present invention is not limited thereto.

The passivation films 190A and 190B may be generally formed on the firstand the second conductive type semiconductor regions 170 and 120 otherthan opening portions 102 and 104 respectively corresponding to thefirst and the second electrodes 150 and 140. Each of the passivationfilms 190A and 190B may be formed of an undoped passivation film notseparately including a dopant.

More specifically, the first passivation film 190A may be generallyformed on (e.g., brought into contact with) the portions of the firstconductive type semiconductor region 170 other than the opening portion102. The second passivation film 190B may be generally formed on (e.g.,brought into contact with) the portions of the second conductive typesemiconductor region 120 other than the opening portion 104.

Furthermore, the anti-reflection layer 130 may be placed on the secondpassivation film 190B.

The passivation films 190A and 190B are brought into contact with andformed on the first and the second conductive semiconductor regions 170and 120, thereby being capable of immobilizing defects present in thefirst and the second conductive type semiconductor regions 170 and 120.

Accordingly, the open voltage Voc of the solar cell can be increasedbecause the recombination sites of minority carriers are removed. Theanti-reflection layer 130 can reduce the reflectance of light incidenton the front surface of the semiconductor substrate 100.

Accordingly, the amount of light reaching the pn junction formed at theinterface of the base region 110 and the first conductive typesemiconductor region 170 can be increased because the reflectance oflight incident through the front surface of the semiconductor substrate100 is lowered. Accordingly, the short circuit current Isc of the solarcell can be increased. As a result, efficiency of the solar cell can beimproved because the open voltage and short circuit current of the solarcell are increased by the passivation films 190A and 190B and theanti-reflection layer 130 as described above.

For example, the passivation film 190A, 190B or the anti-reflectionlayer 130 may have a single film selected from the group consisting of asilicon nitride film, a silicon nitride film including hydrogen, asilicon oxide film, a silicon oxynitride film, an aluminum oxide film,MgF₂, ZnS, TiO₂, and CeO₂ or may have a multi-layer structure in whichtwo or more films selected from the group are combined.

For example, if a contacted conductive semiconductor region of the firstand the second conductive semiconductor regions 170 and 120 has an ntype, a corresponding one of the first and the second passivation films190A and 190B may include a silicon oxide film or a silicon nitride filmhaving fixed positive charges. If the contacted conductive semiconductorregion has a p type, the corresponding passivation film may include analuminum oxide film having fixed negative charges. Furthermore, theanti-reflection layer 130 may include silicon nitride, for example.

More specifically, in an embodiment of the present invention, the firstpassivation film 190A brought into contact with the first conductivetype semiconductor region 170 may be formed of a silicon nitride film,may have a refractive index of 1.9˜2.1, and may have a thickness of 30nm 50 nm.

Furthermore, the second passivation film 190B brought into contact withthe second conductive type semiconductor region 120 may have adual-layer structure in which an aluminum oxide film and a siliconnitride film are sequentially stacked on the second conductive typesemiconductor region 120. In this instance, the aluminum oxide film mayhave a refractive index of 1.5˜1.7 and a thickness of 5 nm˜10 nm. Thesilicon nitride film of the second passivation film 190B may have arefractive index of 1.9˜2.1 and a thickness of 70 nm˜120 nm.

However, the present invention is not limited to the examples. Thepassivation films 190A and 190B and the anti-reflection layer 130 mayinclude various materials.

The first electrode 150 is placed on (e.g., brought into contact with)on the first conductive type semiconductor region 170 and electricallyconnected to the first conductive type semiconductor region 170. Thefirst electrode 150 may be electrically connected to the firstconductive type semiconductor region 170 through the opening portion 102formed in the first passivation film 190A (i.e., by penetrating thefirst passivation film 190A).

In this instance, the first electrode 150 penetrates the firstpassivation film 190A and is connected to the first conductive typesemiconductor region 170, but may be connected to a surface of the firstconductive type semiconductor region 170.

Likewise, the second electrode 140 is placed on (e.g., brought intocontact with) the second conductive type semiconductor region 120 andelectrically connected to the second conductive type semiconductorregion 120. The second electrode 140 may be electrically connected tothe first conductive type semiconductor region 170 through the openingportion 104 formed in the second passivation film 190B and theanti-reflection layer 130 (i.e., through the second passivation film190B and the anti-reflection layer 130).

The first and the second electrodes 150 and 140 may include variousmaterials (more specifically, metal) and may have various shapes.

For example, the first electrode 150 may include a plurality of firstfinger electrodes 151 and a plurality of first bus bars 153, as shown inFIG. 1 .

The plurality of first finger electrodes 151 may be spaced apart fromeach other on the back surface of the first conductive typesemiconductor region 170, may be extended in a first direction x, andmay collect carriers moved toward the first conductive typesemiconductor region 170.

Furthermore, the plurality of first bus bars 153 may be placed on thesame layer as the plurality of first finger electrodes 151 on the firstconductive type semiconductor region 170, may electrically connect theplurality of first finger electrodes 151, and may be extended in asecond direction y crossing the plurality of first finger electrodes151.

Furthermore, the second electrode 140 may include a plurality of secondfinger electrodes 141 and a plurality of second bus bars 143, as shownin FIG. 1 .

The plurality of second finger electrodes 141 may be placed on thesecond conductive type semiconductor region 120, may be electricallyconnected to the second conductive type semiconductor region 120, may bespaced apart from each other, and may be extended in the first directionx.

The plurality of second finger electrodes 141 may collect carriers, forexample, holes moved toward the second conductive type semiconductorregion 120.

Furthermore, the plurality of second bus bars 143 may be placed on thesame layer as the plurality of second finger electrodes 141 on thesecond conductive type semiconductor region 120, may electricallyconnect the plurality of second finger electrodes 141, and may beextended in the second direction y crossing the plurality of secondfinger electrodes 141.

In the solar cell having such a structure, the tunnel layer 160 and thefirst conductive type semiconductor region 170 placed on the backsurface of the semiconductor substrate 100 may be spaced apart from theedge of the back surface of the semiconductor substrate 100 (or the sideof the semiconductor substrate 100) at a first distance D1.

Accordingly, the area of each of the tunnel layer 160 and the firstconductive type semiconductor region 170 may be smaller than the area ofthe semiconductor substrate 100. The first distance D1 may mean theshortest distance of distances between the edge of the back surface ofthe semiconductor substrate 100 and the tunnel layer 160 and the firstconductive type semiconductor region 170.

That is, the isolation portion I in which the tunnel layer 160 and thefirst conductive type semiconductor region 170 (including the firstelectrode 150 connected to the first conductive type semiconductorregion 170 in addition to the tunnel layer 160 and the first conductivetype semiconductor region 170) are not formed may be placed at the edgeof the back surface of the semiconductor substrate 100. In thisinstance, the first passivation film 190A may be formed to cover onesurface of the semiconductor substrate 100, including the isolationportion I.

The isolation portion I may block a contact between the first conductivetype semiconductor region 170 and the second conductive typesemiconductor region 120 in any one of the first surface, side, andsecond surface of the semiconductor substrate 100. For example, theisolation portion I may function as an edge isolator for isolating thefirst conductive type semiconductor region 170 from the edge of the backsurface of the semiconductor substrate 100.

That is, when the second conductive type semiconductor region 120 isformed, the impurities of the second conductive type may be diffusedinto the side of or the edge of the back surface of the semiconductorsubstrate 100, and thus the first conductive type semiconductor region170 and the second conductive type semiconductor region 120 may beunwantedly short-circuited in the side of or the edge of the backsurface of the semiconductor substrate 100. In the present embodiment,such a problem can be fundamentally prevented by removing the firstconductive type semiconductor region 170 from the edge of the backsurface of the semiconductor substrate 100.

Furthermore, the area of the second conductive type semiconductor region120 can be maximized because the second conductive type semiconductorregion 120 is generally formed on the front surface of the semiconductorsubstrate 100.

The isolation portion I may be formed in the entire edge of the backsurface of the semiconductor substrate 100 and may have a closed shape,as shown in FIG. 3 . Furthermore, a specific step or operation ispresent between portions in which the isolation portion I and the tunnellayer 160 and the first conductive type semiconductor region 170 havebeen formed.

For example, the first distance D1 (i.e., the width of the isolationportion I) may be 1 mm or less. If the first distance D1 exceeds 1 mm,efficiency may be deteriorated because the area of the first conductivetype semiconductor region 170 is reduced. For example, the firstdistance D1 may be 1 nm to 1 mm. If the first distance D1 is less than 1mm, the effect of the isolation portion I may not be sufficient.However, the present invention is not limited to the above values. Thefirst distance D1 may have a different value depending on the size ofthe semiconductor substrate 100, for example.

The first conductive type semiconductor region 170 may have a shapehaving a smaller area as the first conductive type semiconductor region170 becomes distant from the semiconductor substrate 100. In thisinstance, the side of the first conductive type semiconductor region 170may be formed to be not vertical to the semiconductor substrate 100(e.g., approximately slanted) as the first conductive type semiconductorregion 170 becomes distant from the semiconductor substrate 100.

That is, as shown in FIG. 2 , the thickness of the edge region of thefirst conductive type semiconductor region 170 may be graduallydecreased toward the isolation portion I.

For example, the area of the first conductive type semiconductor region170 may be reduced as the first conductive type semiconductor region 170becomes distant from the semiconductor substrate 100, so the side of thefirst conductive type semiconductor region 170 may be formed to berounded. The side of the tunnel layer 160 may be placed so that it isextended along with the side of the first conductive type semiconductorregion 170 and may have a rounded shape similar to the first conductivetype semiconductor region 170.

The reason for this is that a wet process is used in the process offorming the isolation portion I by removing the first conductive typesemiconductor region 170 and the tunnel layer 160. This is describedlater. In some embodiments, the sides of the first conductive typesemiconductor region 170 and the tunnel layer 160 may have variousshapes in addition to the rounded shape.

Furthermore, the first passivation film 190A placed on the back surfaceside of the semiconductor substrate 100 may be placed on the firstconductive type semiconductor region 170 in the portion in which thetunnel layer 160 and the first conductive type semiconductor region 170are present and may come into contact with the back surface of thesemiconductor substrate 100 in the isolation portion I.

That is, the first passivation film 190A may be directly brought intocontact with and formed on the back surface of the semiconductorsubstrate 100 near the edge of the semiconductor substrate 100, may beextended from the edge of the semiconductor substrate 100, may bebrought into contact with and formed on the sides of the tunnel layer160 and the first conductive type semiconductor region 170 whilecovering the sides, may be extended from the sides, and may be broughtinto contact with and formed on the top surface of the first conductivetype semiconductor region 170 while covering the top surface.

In an embodiment of the present invention, in the process ofmanufacturing the solar cell, the isolation portion I may be formed byremoving the tunnel layer 160 and the first conductive typesemiconductor region 170 placed in the edge of the back surface of thesemiconductor substrate 100.

Accordingly, the first passivation film 190A may be formed to cover anedge portion of the back surface of the semiconductor substrate 100which has been exposed by removing the tunnel layer 160 and the secondconductive type semiconductor region 160, that is, the isolation portionI.

Accordingly, the isolation portion I can prevent a passivationcharacteristic from being deteriorated. In this instance, the structureof the solar cell and the process of manufacturing the solar cell can besimplified because the first passivation film 190A is used withoutforming a separate film for protecting the isolation portion I.

Furthermore, the first passivation film 190A may include a side portion190Aa extended up to the top of the side of the semiconductor substrate100. If the side portion 190Aa of the first passivation film 190A isused, the first passivation film 190A may be formed to cover the upperside of the back surface of the semiconductor substrate 100 generallyand stably.

Furthermore, the second passivation film 190B and the anti-reflectionlayer 130 may include side portions 190Ba and 130 a extended up to thetop of the side of the semiconductor substrate 100.

In this instance, the second passivation film 190B may be placed closeto the semiconductor substrate 100 on the side of the semiconductorsubstrate 100, and the first passivation film 190A may be placed on thesecond passivation film 190B.

More specifically, the side portion 190Ba of the second passivation film190B may come into contact with the side of the semiconductor substrate100. The side portion 130 a of the anti-reflection layer 130 may comeinto contact with the side portion 190Ba of the second passivation film190B. The side portion 190Aa of the first passivation film 190A may comeinto contact with the side portion 130 a of the anti-reflection layer130.

Accordingly, the second conductive type semiconductor region 120 can bestably passivated because the second passivation film 190B is firstformed and the first passivation film 190A is then formed in the processof forming the first passivation film 190A. This is described in moredetail later.

However, the present invention is not limited to the example. Forexample, at least one of the side portions 190Aa, 190Ba, and 130 a maynot be provided on the side of the semiconductor substrate 100, orsequence in which the side portions 190Aa, 190Ba, and 130 a are stackedmay be changed.

A plane shape of the first electrode 150 is described in detail withreference to FIG. 3 , and a plane shape of the second electrode 140 isthen described in detail.

Referring to FIG. 3 , the first electrode 150 may include the pluralityof first finger electrodes 151 spaced apart from each other at aspecific pitch. In FIG. 3 , the first finger electrodes 151 have beenillustrated as being parallel and as being parallel in the edge of thesemiconductor substrate 100, but the present invention is not limitedthereto.

Furthermore, only one first bus bar 153 may be included. As shown inFIG. 3 , a plurality of the first bus bars 153 having a pitch greaterthan the pitch between the first finger electrodes 151 may be included.

The width of the first bus bar 153 may be greater than the width of thefirst finger electrode 151, but the present invention is not limitedthereto. Accordingly, the width of the first bus bar 153 may be the sameas or smaller than the width of the first finger electrode 151.

When viewed from a cross section, both the first finger electrodes 151and first bus bar 153 of the first electrode 150 may be formed topenetrate the first passivation film 190A. That is, the opening portion102 may be formed in accordance with all of the first finger electrodes151 and first bus bar 153 of the first electrode 150.

However, the present invention is not limited to the example. Forexample, the first finger electrodes 151 of the first electrode 150 maybe formed to penetrate the first passivation film 190A, and the firstbus bar 153 may be formed on the first passivation film 190A. In thisinstance, the opening portion 102 may be formed to have a shapecorresponding to the first finger electrodes 151, but may not be formedin a portion in which only the first bus bar 153 is placed.

As described above, in the present embodiment, the isolation portion Imay be formed in the portion in which the tunnel layer 160 and the firstconductive type semiconductor region 170 are not formed along the edgeof the semiconductor substrate 100. Accordingly, the first electrode 150formed on the first conductive type semiconductor region 170 may not beformed in the isolation portion I.

Accordingly, the ends of the first finger electrodes 151 and bus bar 153of the first electrode 150 may be spaced apart from the edge of thesemiconductor substrate 100 at least at the first distance D1.

Furthermore, the second finger electrodes 141 and second bus bar 142 ofthe second electrode 140 may be respectively formed in accordance withthe first finger electrodes 151 and first bus bar 153 of the firstelectrode 150.

The contents described in connection with the first finger electrodes151 and first bus bar 153 of the first electrode 150 may be applied tothe second finger electrodes 141 and second bus bar 142 of the secondelectrode 140 without a change except the contents described inconnection with the isolation portion I.

Furthermore, the contents related to the first passivation film 190A inthe first electrode 150 may be applied to the second passivation film190B and the anti-reflection layer 130 in the second electrode 140without a change.

In this instance, the width and pitch of the first finger electrodes 151and first bus bar 153 of the first electrode 150 may be the same as ordifferent from the width and pitch of the second finger electrodes 141and second bus bar 142 of the second electrode 140.

However, the present invention is not limited to the example. Forexample, the first electrode 150 and the second electrode 140 may havedifferent plane shapes and may be modified in various ways.

As described above, in the present embodiment, since the first and thesecond electrodes 150 and 140 of the solar cell have a specific pattern,the solar cell has a bi-facial structure in which light may be incidenton the front and back surfaces of the semiconductor substrate 100.

Accordingly, efficiency of the solar cell can be improved because theamount of light used in the solar cell is increased. However, thepresent invention is not limited to the bi-facial structure. Forexample, the solar cell may have a structure in which the firstelectrode 150 is generally formed on the back surface side of thesemiconductor substrate 100 and may have various structures.

In this instance, if the isolation portion I is formed on the backsurface of the semiconductor substrate 100, the first conductive typesemiconductor region 170 and the second conductive type semiconductorregion 120 can be effectively prevented from being unnecessarilyinterconnected.

Furthermore, a surface of the semiconductor substrate 100 on which theisolation portion I is placed may be covered and passivated by the firstpassivation film 190A covering the first conductive type semiconductorregion 170.

Accordingly, problems attributable to surface recombination can beminimized because the isolation portion I is passivated by such a simplestructure. That is, efficiency and reliability of a solar cell can beimproved and a defective ratio of the solar cell can be reduced by thesimple structure.

In the first embodiment of the present invention, an example in whichthe first electrode 150 penetrates the first passivation film 190A andthe first electrode 150 is connected to the first conductive typesemiconductor region 170, but is connected to a surface of the firstconductive type semiconductor region 170 has been described.

In some embodiments, however, the first electrode 150 penetrates thefirst passivation film 190A and is connected to the first conductivetype semiconductor region 170, but at least part of the first electrode150 may be depressed and formed in the first conductive typesemiconductor region 170. This is described in more detail below.

FIGS. 5 to 7 depict a solar cell according to a second embodiment of thepresent invention.

FIG. 5 is a cross-sectional view of the solar cell taken along lineII-II of FIG. 1 . Furthermore, FIG. 6 is an enlarged view of a portion Kin FIG. 5 , and FIG. 7 is a real photograph of a contact portion betweenthe first electrode 150 and the first conductive type semiconductorregion 170.

Furthermore, FIG. 8 depicts a comparison example different from thesecond embodiment of the present invention.

A description of contents redundant with the contents described withreference to FIGS. 1 to 4 is omitted.

For reference, in FIG. 5 , a region that belongs to the first conductivetype semiconductor region 170 and that is placed in the space betweenthe first finger electrode 151 and the tunnel layer 160 is called afinger forming region 170A1. A region that belongs to the firstconductive type semiconductor region 170 and that is placed in the spacebetween the first bus bar 153 and the tunnel layer 160 is called a busbar forming region 170A2. The remaining regions of the first conductivetype semiconductor region 170 other than the finger forming region 170A1and the bus bar forming region 170A2 is called a non-forming region170B. Furthermore, the finger forming region 170A1 and the bus barforming region 170A2 are collectively called an electrode forming region170A.

In the solar cell according to the second embodiment of the presentinvention, at least part of the first electrode 150 may penetrate thefirst passivation film 190A and may be depressed into the firstconductive type semiconductor region 170 and electrically connected tothe first conductive type semiconductor region 170, as shown in FIGS. 5and 6 .

For example, both the first finger electrode 151 and first bus bar 153of the first electrode 150 may be depressed and formed in the firstconductive type semiconductor region 170.

In other words, as shown in FIG. 6 , the location of a first boundarysurface BS1 in which the first conductive type semiconductor region 170and the first electrode 150 come into contact with each other may bemore depressed and formed toward the semiconductor substrate 100 thanthe location of a second boundary surface BS2 in which the firstconductive type semiconductor region 170 and the first passivation film190A come into contact with each other.

Accordingly, the distance between the semiconductor substrate 100 andthe first boundary surface BS1 may be smaller than the distance betweenthe semiconductor substrate 100 and the second boundary surface BS2.

In this instance, all of the plurality of first finger electrodes 151and the first bus bar 153 may be formed to have a single layer or doublelayer structure. In some embodiments, the plurality of first fingerelectrodes 151 may be formed to have a single layer structure, and thefirst bus bar 153 may be formed to have a double layer structure.

In FIG. 6 , the first finger electrode 151 has been illustrated as beingan example. Like the first finger electrode 151, the first bus bar 153may have the same structure in which it has been depressed into thefirst conductive type semiconductor region 170.

As described above, the structure in which the first electrode 150 hasbeen depressed into the first conductive type semiconductor region 170may be formed when a paste for the first electrode perforates the firstpassivation film 190A and penetrates the first conductive typesemiconductor region 170 in a thermal treatment process in the state inwhich the paste for the first electrode for forming the first electrode150 has been patterned and formed on the back surface of the firstpassivation film 190A.

If the first electrode 150 is formed by the process of printing andthermally treating the paste for the first electrode as described above,there are advantages in that a cost is relatively low compared to aplating method and a process time can be reduced.

In this instance, a difference TBS between the heights of the firstboundary surface BS1 and the second boundary surface BS2 may be set to 1nm˜20 nm. The difference between the heights of the first and the secondboundary surfaces BS1 and BS2 may vary depending on the time taken forthe thermal treatment process for forming the first electrode 150 andcontent of frit glass included in the paste for the first electrode.

FIGS. 5 and 6 have illustrated an example in which all of the pluralityof first bus bars 153 and the plurality of first finger electrodes 151forming the first electrode 150 have been depressed into the firstconductive type semiconductor region 170.

However, the present invention is not necessarily limited to theexample. For example, only the plurality of first finger electrodes 151of the first electrode 150 may be depressed and formed in the firstconductive type semiconductor region 170. The example in which only theplurality of first finger electrodes 151 has been depressed into thefirst conductive type semiconductor region 170 as described above isdescribed in detail later with reference to FIG. 9 and related drawings.

Accordingly, in the solar cell according to an embodiment of the presentinvention, as shown in FIG. 6 , the first electrode 150 may be depressedinto the first conductive type semiconductor region 170, and the firstconductive type semiconductor region 170 and the first electrode 150 maycome into contact with each other in the first boundary surface BS1 ofthe first conductive type semiconductor region 170.

In this instance, as shown in FIG. 5 , a plurality of metal crystals MCextracted from the first electrode 150 may be placed in the electrodeforming region 170A of the first conductive type semiconductor region170 in which the first electrode 150 has been formed, as describedabove.

For example, as shown in FIG. 6 , the plurality of metal crystals MCextracted from the first finger electrode 151 may be placed in thefinger forming region 170A1 of the first conductive type semiconductorregion 170 in which the first finger electrode 151 is formed.

Only the electrode finger forming region 170A1 of the electrode formingregion 170A of the first conductive type semiconductor region 170 hasbeen illustrated in FIG. 6 . Likewise, the plurality of metal crystalsMC extracted from the first bus bar 153 may be placed in the bus barforming region 170A2, as shown in FIG. 5 .

The plurality of metal crystals MC has relatively low resistancecompared to the first conductive type semiconductor region 170 made ofpolycrystalline silicon. Accordingly, as shown in FIG. 6 , carrierswhich have moved from the semiconductor substrate 100 to the firstconductive type semiconductor region 170 through the tunnel layer 160,for example, electrons may directly move to the first electrode 150through the metal crystals MC or may jump between the metal crystals MCand the metal crystals MC and move to the first electrode 150.

Accordingly, the plurality of metal crystals MC may function to helpcarriers to move to the first electrode 150 more easily.

Accordingly, the metal crystals MC may narrow a substantial distancebetween the semiconductor substrate 100 and the first electrode 150 dueto its low resistance.

Furthermore, when the first electrode 150 is connected to the firstconductive type semiconductor region 170, the metal crystals MC areformed in the direction of the semiconductor substrate 100 on the basisof the first boundary surface BS1, that is, the boundary of the firstelectrode 150 and the first conductive type semiconductor region 170.Accordingly, contact resistance between the first electrode 150 and thefirst conductive type semiconductor region 170 can be further lowered.

Accordingly, if the plurality of metal crystals MC is further includedin the first conductive type semiconductor region 170 between the firstelectrode 150 and the tunnel layer 160 as in the embodiment of thepresent invention shown in FIG. 6 , efficiency of the solar cell can befurther improved.

As shown in FIG. 5 , the metal crystals MC may be placed in theelectrode forming region 170A of the first conductive type semiconductorregion 170 in which the first electrode 150 has been formed, but may notbe placed in the non-forming region 170B of the first conductive typesemiconductor region 170 in which the first electrode 150 has not beenformed.

The reason why the metal crystals MC are placed in the electrode formingregion 170A of the first conductive type semiconductor region 170, butare not placed in the non-forming region 170B of the first conductivetype semiconductor region 170 as described above is that metal extractedfrom the first electrode 150 during the thermal treatment process forforming the first electrode 150 is recrystallized to form the pluralityof metal crystals MC.

For example, the plurality of first electrodes 150 may be formed toinclude at least one conductive metal material. In this instance, theconductive metal material included in the plurality of first electrodes150 may be at least one selected from the group consisting of nickel(Ni), copper (Cu), silver (Ag), aluminum (Al), tin (Sn), zinc (Zn),indium (In), titanium (Ti), and gold (Au) and a combination of them, forexample, but may include other conductive metal materials.

In this instance, the plurality of metal crystals MC may include thesame metal material as a metal material included in the first electrode150 because the metal crystals MC are formed when the metal materialincluded in the first electrode 150 is extracted and recrystallized.

Accordingly, if the first electrode 150 includes silver (Ag), forexample, the metal crystals MC may also include silver (Ag).

Furthermore, as shown in FIGS. 6 and 7 , the metal crystals MC areplaced in the first conductive type semiconductor region 170, but maynot be placed in the tunnel layer 160.

That is, if the metal crystals MC are placed in the tunnel layer 160 asin the comparison example of FIG. 8 , the functions of the tunnel layer160 may be deteriorated. If the metal crystals MC penetrate the backsurface of the semiconductor substrate 100 through the tunnel layer 160,an open voltage (Voc) characteristic appearing due to the structure ofthe semiconductor substrate 100—the tunnel layer 160—the firstconductive type semiconductor region 170 may be deteriorated, therebybeing capable of deteriorating the semiconductor substrate 100.

If the semiconductor substrate 100 is deteriorated as described above, acharacteristic of the semiconductor substrate 100, for example, acharacteristic, such as a carrier life time, may be deteriorated.

If the metal crystals MC are placed in the first conductive typesemiconductor region 170, but are not placed in the tunnel layer 160 asin the embodiment of the present invention, however, the deteriorationof the characteristic described above can be prevented.

As shown in FIG. 6 , some metal crystals MC1 of the plurality of metalcrystals MC may have a direct contact with the first electrode 150.Furthermore, at least one metal crystal MC2 of the plurality of metalcrystals MC may be spaced apart from the first electrode 150 and placedin the first conductive type semiconductor region 170.

In this instance, the length LMC of the plurality of metal crystals MCfrom the first electrode 150 to the direction of the tunnel layer 160may be ⅔ or less of the thickness of the first conductive typesemiconductor region 170. If the length LMC of the metal crystals MC islimited to ⅔ of the thickness of the first conductive type semiconductorregion 170 as described above, damage to the tunnel layer 160 or thesemiconductor substrate 100 attributable to the excessive length LMC ofthe metal crystals MC can be prevented.

Some of the plurality of metal crystals MC may have a reduced width WMCfrom the first electrode 150 to the direction of the tunnel layer 160.That is, as shown in FIG. 6 or 7 , the width WMC in the surfacedirection (x, y) of a portion that belongs to the metal crystal MC andthat neighbors the first electrode 150 may be smaller than the width ofa portion that belongs to the metal crystal MC and that is adjacent tothe semiconductor substrate 100.

Such a size of the metal crystal MC may be determined in proportion to afiring temperature of the thermal treatment process for forming thefirst electrode 150.

That is, the length or width of the metal crystal MC is characterized inthat it is increased as the firing temperature of thermal treatmentprocess for forming the first electrode 150 rises and it is reduced asthe firing temperature of thermal treatment process for forming thefirst electrode 150 drops. The length or width of the metal crystal MCmay be increased as the width of the first electrode 150, that is, thesource of the metal crystal MC, is increased.

If the firing temperature of the thermal treatment process for formingthe first electrode 150 is excessively low, however, contact resistancebetween the first electrode 150 and the first conductive typesemiconductor region 170 may be increased.

Accordingly, in the second embodiment of the present invention, anexample in which all of the first finger electrodes 151 and first busbar 153 of the first electrode 150 have been depressed into the firstconductive type semiconductor region 170 and the metal crystals MC havebeen formed in both the finger forming region 170A1 and bus bar formingregion 170A2 of the first conductive type semiconductor region 170 hasbeen described. In order to further improve efficiency of the solarcell, only the first finger electrodes 151 may be depressed into thefirst conductive type semiconductor region 170 and the metal crystals MCmay be placed only in the finger forming region 170A1, but may not beplaced in the bus bar forming region 170A2. This is described in detailbelow with reference to FIGS. 9 to 11 .

FIG. 9 is a diagram illustrating a solar cell according to a thirdembodiment of the present invention.

In a description related to FIG. 9 , a description of portions redundantwith the contents described in connection with the second embodiment isomitted, and portions different from the contents of the secondembodiment are chiefly described.

As shown in FIG. 9 , in the solar cell according to the third embodimentof the present invention, at least part of the first electrode 150 maybe depressed and formed in the first conductive type semiconductorregion 170, but only the plurality of first finger electrodes 151 of thefirst electrode 150 may penetrate the first passivation film 190A andmay be depressed and formed in the first conductive type semiconductorregion 170.

In this instance, the metal crystals MC may be formed only in the fingerforming region 170A1 of the first conductive type semiconductor region170, and the plurality of first bus bars 153 may not be depressed intothe first conductive type semiconductor region 170, but may be formed onthe back surface of the first passivation film 190A.

Accordingly, the metal crystals MC may not be formed in the bus barforming region 170A2 of the first conductive type semiconductor region170.

As described above, only the plurality of first finger electrodes 151 ofthe first electrode 150 may penetrate the first passivation film 190Aand may be depressed into the first conductive type semiconductor region170 so that the metal crystals MC are formed only in the finger formingregion 170A1 of the first conductive type semiconductor region 170, andthe first bus bar 153 may be formed on the first passivation film 190A.

As described above with reference to FIGS. 6 to 8 , if the metalcrystals MC are not formed in the bus bar forming region 170A2 of thefirst conductive type semiconductor region 170 as described above, themetal crystals MC are not placed in the tunnel layer 160, and thus therecan be prevented the phenomenon in which the semiconductor substrate 100is deteriorated because the metal crystals MC penetrate the tunnel layer160 and are connected to the semiconductor substrate 100.

More specifically, the width of the first bus bar 153 is relativelygreater than the width of the first finger electrode 151 as describedabove with reference to FIGS. 1 and 5 . Accordingly, in the thermaltreatment process, the metal crystals MC having a relatively greatlength or width may penetrate the tunnel layer 160 and may beshort-circuited with the semiconductor substrate 100, as shown in FIG. 8. Accordingly, the semiconductor substrate 100 may be deteriorated. Ifthe metal crystals MC are not formed in the bus bar forming region 170A2of the first conductive type semiconductor region 170, such adeterioration phenomenon can be prevented.

Accordingly, the solar cell according to the third embodiment of thepresent invention has a structure in which only the first fingerelectrodes 151 of the first finger electrodes 151 and first bus bar 153of the first electrode 150 penetrate the first passivation film 190A andare depressed and formed in the first conductive type semiconductorregion 170. Accordingly, only the first conductive type semiconductorregion 170 and the first finger electrodes 151 come into contact witheach other in the first boundary surface BS1 of the first conductivetype semiconductor region 170, the plurality of metal crystals MC may beplaced only in the finger forming region 170A1 which belongs to theelectrode forming region 170A of the first conductive type semiconductorregion 170 and in which the first finger electrode 151 is formed, andthe plurality of metal crystals MC may not be placed in the bus barforming region 170A2 of the first conductive type semiconductor region170 which overlaps the first bus bar 153.

To this end, in an embodiment of the present invention, the plurality offirst finger electrodes 151 and the plurality of first bus bars 153 mayhave different compositions.

More specifically, content of frit glass per unit volume, which isincluded in the plurality of first bus bars 153, may be smaller thancontent of frit glass per unit volume, which is included in theplurality of first finger electrodes 151, or content of frit glass maynot be included in the plurality of first bus bars 153.

Accordingly, in the thermal treatment process for forming the firstelectrode 150, while the plurality of metal crystals MC is extractedinto the finger forming region 170A1 when the first finger electrode 151penetrates the first passivation film 190A and is depressed into thefirst conductive type semiconductor region 170, the first bus bar 153can be prevented from penetrating the first passivation film 190A andfrom being depressed into the first conductive type semiconductor region170 or such a depression can be minimized.

Moreover, although the first bus bar 153 penetrates the firstpassivation film 190A and is depressed into the first conductive typesemiconductor region 170, the deterioration phenomenon in which themetal crystals MC extracted from the first bus bar 153 penetrate thetunnel layer 160 and are short-circuited with the semiconductorsubstrate 100 as shown in FIG. 8 can be prevented.

In this instance, the deterioration of the semiconductor substrate 100may be checked from FIGS. 10 and 11 .

FIG. 10 is a comparison example photograph of the degree of thedeterioration of the semiconductor substrate 100 according to firingtemperatures in the thermal treatment process, which was taken throughphoto luminescence (PL), if the material of a paste for the first busbar is the same as the material of a paste for the first fingerelectrode. FIG. 11 is photograph of the degree of the deterioration ofthe semiconductor substrate 100 according to firing temperatures in thethermal treatment process, which was taken through photo luminescence(PL), if the material of a paste 153P for the first bus bar is differentfrom the material of a paste for the first finger electrodes inaccordance with the third embodiment of the present invention.

From the PL images showing the open voltages Voc of the semiconductorsubstrate 100, the deterioration phenomenon occurring because the metalcrystals MC penetrate the tunnel layer 160 and are short-circuited withthe semiconductor substrate 100 depending on the temperature of thethermal treatment process can be checked.

As some region of the semiconductor substrate 100 becomes darker in thePL image, it means the open voltage is reduced and thus thedeterioration of the semiconductor substrate 100 is increased. As someregion of the semiconductor substrate 100 becomes brighter, it meansthat the open voltage is sufficiently high and thus the deterioration ofthe semiconductor substrate 100 is reduced or is not present.

More specifically, if a shade region is increased in the PL image as thetemperature of the thermal treatment process rises, it means that theopen voltage is reduced and the deterioration of the semiconductorsubstrate 100 is increased because the metal crystals MC penetrate thetunnel layer 160 and are short-circuited with the semiconductorsubstrate 100. If a shade region is not increased in the PL image as thetemperature of the thermal treatment process rises, it means that theopen voltage is sufficiently high and the deterioration of thesemiconductor substrate 100 is small or is almost not present becausethe metal crystals MC do not penetrate the tunnel layer 160 or thesemiconductor substrate 100.

In FIGS. 10 and 11 , images of the paste 153P for the first bus barhaving a relatively great width have been illustrated, but images of apaste for the first finger electrodes having a very small width are notillustrated. The paste for the first finger electrodes may intersect thepaste 153P for the first bus bars and may be formed.

FIG. 10 shows an instance where the paste 153P for the first bus barshaving the same material as the paste for the first finger electrodeswas used, and FIG. 11 shows an instance where the paste 153P for thefirst bus bars having a material different from the material of thepaste for the first finger electrodes as described above with referenceto FIG. 9 was used.

In FIG. 10 , the paste 153P for the first bus bars and the paste for thefirst finger electrodes have the same material. Accordingly, the paste153P for the first bus bars may also penetrate the first passivationfilm 190A and may be depressed and formed in the first conductive typesemiconductor region 170, so the metal crystals MC may be formed in thebus bar forming region 170A2 of the first conductive type semiconductorregion 170.

Accordingly, if the temperature of the thermal treatment process forforming the first electrode 150 is relatively low, for example, about820° C. or 795° C. as shown in (c) and (d) of FIG. 10 , thesemiconductor substrate 100 is not deteriorated because there is almostno metal crystal MC which is extracted from the paste for the firstelectrode and subsides into the first conductive type semiconductorregion 170. In this instance, efficiency of the solar cell may bereduced because contact resistance of the first finger electrodes 151may be relatively high.

If the temperature of the thermal treatment process for forming thefirst electrode 150 is relatively high, for example, about 870° C. or845° C. as shown in (a) and (b) of FIG. 10 , the shade region isincreased in the semiconductor substrate 100 and the deterioration ofthe semiconductor substrate 100 is relatively increased.

The reason for this is that the deterioration of the semiconductorsubstrate 100 is increased because the metal crystals MC extracted fromthe paste 153P for the first bus bars are placed in the first conductivetype semiconductor region 170 and such metal crystals MC penetrate thetunnel layer 160 and are connected to the semiconductor substrate 100.

As described above with reference to FIG. 9 , if the first fingerelectrodes 151 and the first bus bar 153 are made of different materialsin accordance with the third embodiment of the present invention, it maybe seen that the shade region of the semiconductor substrate 100 israrely increased even in (a) and (b) of FIG. 11 in which the temperatureof the thermal treatment process is relatively high as well as in (c)and (d) of FIG. 11 in which the temperature of the thermal treatmentprocess is relatively low.

The reason for this is that the semiconductor substrate 100 is notdeteriorated because the paste 153P for the first bus bars does notpenetrate the first passivation film 190A or although the paste 153P forthe first bus bars penetrates the first passivation film 190A andconnects to the first conductive type semiconductor region 170 and thusthe metal crystals MC are formed in the first conductive typesemiconductor region 170, the metal crystals MC are not placed in thetunnel layer 160 if the paste 153P for the first bus bars and the pastefor the first finger electrodes are made of different materials.

As described above, the solar cell according to the third embodiment ofthe present invention can prevent the deterioration of the semiconductorsubstrate 100 and have further improved efficiency because the solarcell maintains a sufficient high open voltage Voc by forming the firstfinger electrodes 151 and the first bus bar 153 using differentmaterials.

The structures of the solar cells according to embodiments of thepresent invention have been described so far. Hereinafter, methods formanufacturing solar cells are described.

FIG. 12 is a flowchart illustrating an example of a method formanufacturing a solar cell according to a first embodiment of thepresent invention. FIGS. 13A to 13J are cross-sectional views of themethod for manufacturing a solar cell according to the flowchart of FIG.12 .

Furthermore, FIG. 14 is a diagram illustrating a modified example of themethod for manufacturing a solar cell according to the first embodiment.FIG. 15 is a diagram illustrating another modified example of the methodfor manufacturing a solar cell according to the first embodiment.

As shown in FIG. 12 , an example of the method for manufacturing a solarcell according to the first embodiment of the present invention mayinclude a tunnel layer forming step (operation) S1, an intrinsicsemiconductor layer forming step (operation) S2, a first conductive typesemiconductor region forming step (operation) S3, a removing step(operation) S4, a second conductive type semiconductor region formingstep (operation) S5, an anti-reflection layer and second passivationfilm forming step (operation) S6, a first passivation film forming step(operation) S7, and an electrode forming step (operation) S8.

In this example, the removing step S4 and the anti-reflection layer andsecond passivation film forming step S6 have been illustrated as beingincluded. In some embodiments, the removing step S4 and theanti-reflection layer and second passivation film forming step S6 may beomitted.

An example in which the removing step S4 and the anti-reflection layerand second passivation film forming step S6 are included, forconvenience of description, is described below.

As a preliminary step (operation) for manufacturing a solar cellaccording to the first embodiment of the present invention, theconcave-convex portions may be formed by performing a texturing processon the front and back surfaces of the semiconductor substrate 100, asshown in FIG. 13A.

Wet or dry texturing may be used as the texturing technique for thesemiconductor substrate 100.

The wet texturing may be performed by dipping the semiconductorsubstrate 100 into a texturing solution and is advantageous in that theprocess time is short. The dry texturing may be performed by cutting asurface of the semiconductor substrate 100 using a diamond grill or alaser. In the dry texturing, the concave-convex portions may beuniformly formed, but the process time is long and the semiconductorsubstrate 100 may be damaged.

In addition, the semiconductor substrate 100 may be textured usingreactive ion etch (RIE). As described above, in an embodiment of thepresent invention, the semiconductor substrate 100 may be textured usingvarious methods.

For a simple illustration, concave-convex portions have been illustratedas being not formed on the side of the semiconductor substrate 100 bythe texturing. Furthermore, it may be difficult to clearly recognize theconcave-convex portions by the texturing because the semiconductorsubstrate 100 has a very small thickness.

However, the present invention is not limited to the above description.For example, the concave-convex portions according to the texturing maybe provided on the side of the semiconductor substrate 100. Furthermore,the texturing of the semiconductor substrate 100 may be performed in asubsequent process.

As shown in FIG. 12 , the tunnel layer forming step S1 for forming thetunnel layer 160 on one surface of the semiconductor substrate 100 maybe performed in the state in which the concave-convex portions have beenprovided in the semiconductor substrate 100 as described above.

In the tunnel layer forming step S1, for example, as shown in FIG. 13B,the tunnel layer 160 may be generally formed on one surface and theother surface of the semiconductor substrate 100. In this instance, thetunnel layer 160 may also be generally formed on the side of thesemiconductor substrate 100.

If the tunnel layer 160 is generally formed on the surfaces of thesemiconductor substrate 100 as described above, the tunnel layer 160formed on the other surface (i.e., the front surface) and side of thesemiconductor substrate 100 may be removed in the removing step S4.

If the tunnel layer 160 is formed on only one surface of thesemiconductor substrate 100, the removing step S4 may be omitted.

In this instance, the tunnel layer 160 may be formed by thermaloxidation, chemical oxidation, or deposition (e.g., an atmosphericpressure chemical vapor deposition (APCVD) method or a low-pressurechemical vapor deposition (LPCVD) method), for example. Additionally,after the tunnel layer 160 having a thin thickness is formed, thethickness or density of the tunnel layer 160 may be increased bysubsequent thermal treatment within a furnace.

However, the present invention is not limited to such methods. Thetunnel layer 160 may be formed by various other methods. In thisinstance, the tunnel layer 160 may be formed of a silicon oxide layer.

For example, in the present embodiment, the tunnel layer 160 may beformed in a gas atmosphere, including a source gas, at a temperaturehigher than normal temperature and pressure smaller than atmosphericpressure. In the present embodiment, the source gas includes an oxygengas, and thus the tunnel layer 160 may be formed of an oxide layer.

More specifically, at a high temperature, the tunnel layer 160 may beformed of a thermal oxide (e.g., thermal silicon oxide) layer formed bya reaction of oxygen and the semiconductor material (e.g., silicon) ofthe semiconductor substrate 100.

In the present embodiment, the source gas does not include all sourcematerials forming the tunnel layer 160, but may include only an oxygengas of the oxide forming the tunnel layer 160 and may not include othersource materials.

For example, if the tunnel layer 160 includes silicon oxide, it includesonly an oxygen gas as the source gas, but does not include a gasincluding silicon, that is, other source material. Accordingly, thetunnel layer 160 may be formed by a thermal oxidation process in whichoxygen included in the oxygen gas is diffused into the semiconductorsubstrate 100 and reacts with the semiconductor material.

In some embodiments, in a deposition process, a silane (SiH₄) gasincluding silicon, together with an oxygen gas including oxygen, may besupplied as the source gas. In this instance, oxygen separated from theoxygen gas may chemically react with silicon separated from the silanegas by thermal decomposition, thereby being capable of forming siliconoxide. When the tunnel layer 160 is formed, a gas atmosphere may includevarious gases in addition to the oxygen gas, that is, the source gas.

Furthermore, pressure when the tunnel layer 160 is formed may be lowerthan atmospheric pressure. In this instance, although the tunnel layer160 is formed by a thermal oxidation process using a relatively hightemperature (e.g., 600° C. or more), the tunnel layer 160 can maintainlow growth speed due to the low pressure. Accordingly, the thickness ofthe tunnel layer 160 can be significantly reduced.

For example, when the tunnel layer 160 is formed, a temperature may beset to 600° C. to 800° C. and pressure may be set to 600 Torr or less inorder to effectively control the thickness of the tunnel layer 160.

As described above, in the present embodiment, when the tunnel layer 160is formed, both the temperature and pressure need to be controlled.Accordingly, the tunnel layer 160 according to the present embodimentmay not be formed in a conventional furnace whose pressure cannot becontrolled, and the tunnel layer 160 has to be formed in an apparatuswhose temperature and pressure can be controlled.

Accordingly, in the present embodiment, the tunnel layer 160 may beformed by a thermal oxidation process within deposition apparatus. Inthis instance, since low pressure needs to be implemented, the tunnellayer 160 may be formed in a low-pressure chemical vapor depositionapparatus.

An intrinsic semiconductor layer 170′ formed on the tunnel layer 160 isformed by a deposition apparatus. Accordingly, if the tunnel layer 160is formed in the deposition apparatus, the tunnel layer 160 and theintrinsic semiconductor layer 170′ can be formed by an in-situ processfor consecutively forming the tunnel layer 160 and the intrinsicsemiconductor layer 170′ in the same deposition apparatus (morespecifically, a low-pressure chemical vapor deposition apparatus).

If the tunnel layer 160 and the intrinsic semiconductor layer 170′ areformed by an in-situ process as described above, a manufacturing costand a manufacturing time can be significantly reduced because themanufacturing process is significantly simplified.

A temperature within the deposition apparatus is controlled by applyingheat (e.g., heating) or removing heat (e.g., cooling) for a long time,and a lot of time is taken to stabilize the temperature. In contrast, agas atmosphere and pressure may be controlled by the type and amount ofgas supplied to the deposition apparatus. Accordingly, a gas atmosphereand pressure can be more easily controlled than a temperature.

In the present embodiment, a difference between a temperature at whichthe tunnel layer 160 is formed and a temperature in the process ofdepositing the intrinsic semiconductor layer 170′ may be set to 200° C.or less (i.e., 0° C. to 200° C.). More specifically, a differencebetween a temperature at which the tunnel layer 160 is formed and atemperature in the process of depositing the intrinsic semiconductorlayer 170′ may be set to 100° C. or less (i.e., 0° C. to 100° C.).

The reason for this is that a difference between a temperature at whichthe tunnel layer 160 is formed and a temperature in the process ofdepositing the intrinsic semiconductor layer 170′ can be reduced becausethe tunnel layer 160 is formed at low pressure and thus the temperatureat which the tunnel layer 160 is formed can be relatively raised.Accordingly, efficiency of the in-situ process of consecutively formingthe tunnel layer 160 and the intrinsic semiconductor layer 170′ can befurther improved because a temperature that is relatively difficult tocontrol can be maintained without a great change or variance asdescribed above.

In contrast, a gas atmosphere in the process of depositing the intrinsicsemiconductor layer 170′ may be different from a gas atmosphere when thetunnel layer 160 is formed, and pressure in the process of depositingthe intrinsic semiconductor layer 170′ may be the same as or differentfrom pressure when the tunnel layer 160 is formed. This is described inmore detail later in a subsequent description of the deposition processof the intrinsic semiconductor layer 170′.

After the tunnel layer forming step S1 is completed as described above,the intrinsic semiconductor layer forming step S2 for forming theintrinsic semiconductor layer 170′ on the tunnel layer 160 formed on onesurface of the semiconductor substrate 100 may be performed as shown inFIG. 12 .

For example, as shown in FIG. 13C, in the intrinsic semiconductor layerforming step S2, the intrinsic semiconductor layer 170′ may be generallyformed on the tunnel layer 160 formed on one surface and the othersurface of the semiconductor substrate 100. In this instance, theintrinsic semiconductor layer 170′ may also be generally formed on thetunnel layer 160 placed on the side of the semiconductor substrate 100.

If the intrinsic semiconductor layer 170′ is placed on both sides of thesemiconductor substrate 100 as described above, the doping and damage ofthe front surface of the semiconductor substrate 100 can be effectivelyprevented in the process of doping the intrinsic semiconductor layer170′ in order to form the first conductive type semiconductor region170.

In the present embodiment, the intrinsic semiconductor layer 170′ may beformed by chemical vapor deposition. More specifically, the intrinsicsemiconductor layer 170′ may be formed by low-pressure chemical vapordeposition.

Accordingly, the intrinsic semiconductor layer 170′ may be formed by thetunnel layer 160 and the in-situ process as described above, but thepresent invention is not limited thereto. The in-situ process may not beapplied to the tunnel layer 160 and the intrinsic semiconductor layer170′.

A gas used in the process of depositing the intrinsic semiconductorlayer 170′ may include a gas (e.g., a silane gas) including asemiconductor material which forms the intrinsic semiconductor layer170′. In the present embodiment, since the intrinsic semiconductor layer170′ is deposited so that the gas atmosphere has the intrinsic property,the gas atmosphere may include only the gas including the semiconductormaterial.

Accordingly, a supply gas can be simplified, and the purity of theformed intrinsic semiconductor layer 170′ can be improved, but thepresent invention is not limited thereto. A separate gas foraccelerating the deposition process of the intrinsic semiconductor layer170′ or improving the characteristics of the intrinsic semiconductorlayer 170′ may be further used.

Furthermore, in the deposition process of the intrinsic semiconductorlayer 170′, the size of a crystal grain and crystallizability may becontrolled by injecting the gas, including the semiconductor material,along with a nitrogen oxide (N₂O) gas and/or an oxygen (O₂) gas.

The deposition temperature of the intrinsic semiconductor layer 170′ maybe the same as or lower than a temperature when the tunnel layer 160 isformed. In particular, if the deposition temperature of the intrinsicsemiconductor layer 170′ is lower than a temperature when the tunnellayer 160 is formed, a characteristic of the intrinsic semiconductorlayer 170′ which directly takes part in photoelectric conversion canbecome uniform.

In some embodiments, the deposition temperature of the intrinsicsemiconductor layer 170′ may be 500° C. to 700° C. Such a depositiontemperature is suitable for depositing the intrinsic semiconductor layer170′ having a crystal structure different from that of the semiconductorsubstrate 100.

The temperature of the tunnel layer 160 is set to be the same as orsimilar to the deposition temperature of the intrinsic semiconductorlayer 170′ as described above. Accordingly, the process can besimplified because the time taken to control a temperature and the timetaken to stabilize a temperature are not required.

Furthermore, deposition pressure of the intrinsic semiconductor layer170′ may be lower than atmospheric pressure, for example, 600 Torr orless (e.g., 1 Torr to 600 Torr). To maintain the deposition pressureless than 1 Torr may be limited on the nature of the process, and thedeposition pressure of less than 1 Torr may be difficult to apply toactual mass production because the process time of the intrinsicsemiconductor layer 170′ is greatly increased.

If the deposition pressure exceeds 600 Torr, the uniformity of theintrinsic semiconductor layer 170′ may be deteriorated. In someembodiments, the deposition pressure of the intrinsic semiconductorlayer 170′ may be the same as or smaller than pressure when the tunnellayer 160 is formed.

In particular, if the deposition pressure of the intrinsic semiconductorlayer 170′ is smaller than pressure when the tunnel layer 160 is formed,a characteristic of the intrinsic semiconductor layer 170′ whichdirectly takes part in photoelectric conversion can become uniform.

This is described in more detail. A gas including a semiconductormaterial (e.g., silicon) is thermally decomposed and the semiconductormaterial is deposited on the tunnel layer 160, thereby being capable offorming the intrinsic semiconductor layer 170′.

If a temperature and/or pressure of the intrinsic semiconductor layer170′ are increased in order to increase deposition speed, thedistribution of crystallizability within the intrinsic semiconductorlayer 170′ is increased. If the distribution of crystallizability withinthe intrinsic semiconductor layer 170′ is increased, the characteristicsof the intrinsic semiconductor layer 170′ may not become uniform becausethe crystallizability of the intrinsic semiconductor layer 170′ takespart in moving speed of carriers.

In contrast, the tunnel layer 160 is formed in a very thin thickness,and the crystallizability of the tunnel layer 160 does not have aninfluence on the characteristics of the tunnel layer 160. Although theintrinsic semiconductor layer 170′ needs to be formed in a thickerthickness than the tunnel layer 160, the deposition temperature and/orpressure of the intrinsic semiconductor layer 170′ are set to be smallerthan those when the tunnel layer 160 is formed in order to improve thecharacteristics of the intrinsic semiconductor layer 170′.

However, the present invention is not limited to such an example. A gasatmosphere, temperature, and pressure of the intrinsic semiconductorlayer 170′ may be changed in various ways.

As described above, the intrinsic semiconductor layer 170′ may be formedby changing the type of gas supplied after the tunnel layer 160 isformed and controlling the amount of a supplied gas.

For example, the intrinsic semiconductor layer 170′ may be formed byremoving a gas (e.g., an oxygen gas, a nitrogen gas, or a chlorine gas),used when the tunnel layer 160 is formed after the tunnel layer 160 isformed, by pumping and purging, and then injecting a gas (e.g., a gasincluding a semiconductor material) for forming the intrinsicsemiconductor layer 170′.

Accordingly, the process of forming the tunnel layer 160 and theintrinsic semiconductor layer 170′ can be simplified. Furthermore, ifthe semiconductor substrate 100 on which the tunnel layer 160 has beenformed is taken out from an apparatus after the tunnel layer 160 isformed as in a prior art, there is a problem in that the tunnel layer160 is contaminated by impurities or the thickness of the tunnel layer160 is increased due to an additional oxidation.

In the present embodiment, the tunnel layer 160 is not externallyexposed until the intrinsic semiconductor layer 170′ is formed becausethe intrinsic semiconductor layer 170′ is consecutively formed in anapparatus in which the tunnel layer 160 has been formed. Accordingly, aproblem occurring because the tunnel layer 160 is externally exposedbefore the intrinsic semiconductor layer 170′ is formed can beprevented.

For reference, if plasma-enhanced chemical vapor deposition (PECVD) isused, a separate crystallization annealing process needs to be performedso that the intrinsic semiconductor layer 170′ has a polycrystallinestructure after it is formed. Accordingly, the structure becomescomplicated, and performance may be deteriorated. Furthermore, sincePECVD is a one-sided process, it may be difficult to generally form theintrinsic semiconductor layer 170′ on both sides of the semiconductorsubstrate 100.

Thereafter, as shown in FIG. 12 , the first conductive typesemiconductor region forming step S3 may be performed.

In the first conductive type semiconductor region forming step S3, thefirst conductive type semiconductor region 170 may be formed by dopingimpurities of the first conductive type into the intrinsic semiconductorlayer 170′ formed on one surface of the semiconductor substrate 100.

More specifically, in the first conductive type semiconductor regionforming step S3, as shown in FIG. 13D, a first conductive typesemiconductor region 170′a may be formed on the entire surface of thesemiconductor substrate 100 by doping impurities of the first conductivetype into the intrinsic semiconductor layer 170′ formed on the entiresurface of the semiconductor substrate 100.

In this instance, in the present embodiment, the impurities of the firstconductive type may be doped using a thermal diffusion method. Thereason for this is that the thermal diffusion method is capable ofdoping while minimizing the deterioration of the characteristics of thetunnel layer 160. In contrast, if an ion implantation method is used,the characteristics of the tunnel layer 160 may be deteriorated due toactivation thermal treatment performed at high temperature after ionimplantation.

For example, as shown in FIG. 13D, the first conductive typesemiconductor region 170′a may be generally formed by thermal treatmentin a gas atmosphere including the impurities of the first conductivetype.

If the first conductive type semiconductor region 170′a has an n type,thermal treatment may be performed in a gas atmosphere including POCl₃.If the first conductive type semiconductor region 170′a has a p type,thermal treatment may be performed in a gas atmosphere including BBr₃.

The process of forming the first conductive type semiconductor region170′a can be simplified using a gas including the impurities of thefirst conductive type as described above. In this instance, doping maybe performed on the front surface and side of the semiconductorsubstrate 100 in addition to the back surface of the semiconductorsubstrate 100 due to such a process.

In the present embodiment, since portions of the intrinsic semiconductorlayer 170′ to be removed in a subsequent process are present on thefront surface and side of the semiconductor substrate 100, a problem inthat the front surface and side of the semiconductor substrate 100 areunnecessarily doped with the impurities of the first conductive type canbe fundamentally prevented.

In an alternative embodiment, that is, a modified example, as shown inFIG. 14 , the first conductive type semiconductor region 170′a may beformed by forming a first doping layer 210, including impurities of thefirst conductive type, on the intrinsic semiconductor layer 170′ placedat least on the back surface side of the semiconductor substrate 100 anddiffusing the impurities of the first conductive type included in thefirst doping layer 210 through thermal treatment.

For example, the first doping layer 210 may include phosphorous silicateglass (PSG) or boron silicate glass (BSG). The first doping layer 210may be easily formed by deposition.

For example, the first doping layer 210 may be formed by atmosphericpressure chemical vapor deposition and may be formed on the back surfaceand/or side of the semiconductor substrate 100, but may not be formed onthe front surface of the semiconductor substrate 100. Accordingly, thefirst conductive type semiconductor region 170′a may be formed on onlythe back surface and/or side of the semiconductor substrate 100, and theintrinsic semiconductor layer 170′ may remain intact on the frontsurface of the semiconductor substrate 100.

Next, as shown in FIG. 13E, a mask layer 202 may be formed on the firstconductive type semiconductor region 170′a placed on the back surfaceside of the semiconductor substrate 100 so that the mask layer 202corresponds to the first conductive type semiconductor region (170 inFIG. 13F) to be left other than the isolation portion (I in FIG. 13F,hereinafter the same).

More specifically, the area of the mask layer 202 may be smaller thanthat of the semiconductor substrate 100. Accordingly, the firstconductive type semiconductor region (170 in FIG. 13F) that remainsother than the isolation portion I may have a smaller area than thesemiconductor substrate 100 by removing an unwanted portion of the firstconductive type semiconductor region 170′a.

For example, the mask layer 202 may be spaced apart from each side (orthe edge) of the semiconductor substrate 100 at a specific seconddistance D2. If the area of the mask layer 202 is the same as or greaterthan the area of the semiconductor substrate 100, it may be difficult toeffectively remove the unwanted portion of the first conductive typesemiconductor region 170′a which is adjacent to the side of thesemiconductor substrate 100 on the back surface side of thesemiconductor substrate 100.

The second distance D2 may be controlled so that the first distance D1between the first conductive type semiconductor region 170′a and theedge of the back surface of the semiconductor substrate 100 has arequired value. For example, the second distance D2 may have a value of1 mm or less (e.g., 1 nm to 1 mm) so that the first distance D1 has avalue of 1 mm or less (e.g., 1 nm to 1 mm), but the present invention isnot limited thereto. The second distance D2 may have values other than 1mm or less.

The mask layer 202 may include a material which is not removed in theprocess of removing part (i.e., the edge D2 of the other surface, side,or one surface of the semiconductor substrate 100) of the firstconductive type semiconductor region 170′a including the semiconductormaterial.

For example, the mask layer 202 not etched by an etch solution which isused in the process of removing part of the first conductive typesemiconductor region 170′a may include oxide, nitride, or resin. Forexample, the mask layer 202 may be formed of a silicon nitride layer sothat the mask layer 202 is formed by a simple process.

As shown in FIG. 12 , the removing step S4 may be performed prior to thesecond conductive type semiconductor region forming step S5 after thefirst conductive type semiconductor region forming step S3.

In the removing step S4, for example, the tunnel layer 160 and theintrinsic semiconductor layer 170′ or the first conductive typesemiconductor region 170′a placed on the other surface of thesemiconductor substrate 100 in FIG. 13E may be removed.

Furthermore, in the removing step S4, portions of the first conductivetype semiconductor region 170′a and the tunnel layer 160 not covered bythe mask layer 202 in FIG. 13E may be removed, so the isolation portionI may be formed.

The tunnel layer 160 and the first conductive type semiconductor region170′a are moved as described above, so the tunnel layer 160 and thefirst conductive type semiconductor region 170, such as those shown inFIG. 13F, may be formed.

In the removing step S4, wet etch using an alkali solution (e.g., a KOHsolution), for example, may be performed on the first conductive typesemiconductor region 170′a and the tunnel layer 160.

In accordance with such wet etch, the first conductive typesemiconductor region 170′a and the tunnel layer 160 placed in theisolation portion I on the front surface, side, or back surface of thesemiconductor substrate 100 can be removed by a simple and easy process.

The first conductive type semiconductor region 170′a may be removedselectively and easily using the alkali solution. The tunnel layer 160having a very small thickness, albeit being an oxide, may also beremoved when the first conductive type semiconductor region 170′a isremoved.

Accordingly, as shown in FIG. 13F, the first conductive typesemiconductor region 170 and the tunnel layer 160 each formed to have asmaller area than the semiconductor substrate 100 and spaced apart fromthe edge of the back surface of the semiconductor substrate 100 at thefirst distance D1 may be formed.

The first conductive type semiconductor region 170 and the tunnel layer160 may have a shape having an area reduced as they become distant fromthe semiconductor substrate 100 and the sides thereof may be formed tobe rounded by the wet etch.

However, the present invention is not limited to the above description.Part of the first conductive type semiconductor region 170 and thetunnel layer 160 may be removed by various methods, such as RIE and dryetch, and the first conductive type semiconductor region 170 and thetunnel layer 160 may have a different shape.

The mask layer 202 may be removed after part of the first conductivetype semiconductor region 170 and the tunnel layer 160 is removed sothat the isolation portion I is formed. The mask layer 202 may beremoved by various methods depending on a material.

For example, if the mask layer 202 includes an oxide or a nitride, itmay be removed by a process using diluted hydrofluoric acid. The masklayer 202 may be removed by a separate process or may be naturallyremoved by a cleaning process including a solution including dilutedhydrofluoric acid.

After the removing step S4 is performed as described above, as shown inFIG. 12 , the second conductive type semiconductor region forming stepS5 for forming the second conductive type semiconductor region 120 bydoping impurities of the second conductive type on the other surface ofthe semiconductor substrate 100 may be performed.

More specifically, as shown in FIG. 13G, in the second conductive typesemiconductor region forming step S5, the second conductive typesemiconductor region 120 may be formed by doping impurities of thesecond conductive type on the front surface side of the semiconductorsubstrate 100.

The second conductive type semiconductor region 120 may be formed byknown various methods. For example, the second conductive typesemiconductor region 120 may be formed by a thermal diffusion method.The reason for this is that the thermal diffusion method is capable ofdoping while minimizing the deterioration of the characteristics of thetunnel layer 160. In contrast, if an ion implantation method is used,the characteristics of the tunnel layer 160 may be deteriorated due toactivation thermal treatment performed at high temperature after ionimplantation.

If the thermal diffusion method is used, in the second conductive typesemiconductor region forming step S5, as shown in FIG. 13G; the secondconductive type semiconductor region 120 may be formed on the frontsurface of the semiconductor substrate 100 by forming a capping film 204on the side and back surface of the semiconductor substrate 100 andperforming thermal treatment in a gas atmosphere including impurities ofthe second conductive type.

If the second conductive type semiconductor region 120 has a p type, thethermal treatment may be performed in a gas atmosphere including BBr₃.If the second conductive type semiconductor region 120 has an n type,the thermal treatment may be performed in a gas atmosphere includingPOCl₃. After the second conductive type semiconductor region 120 isformed through such thermal treatment, the capping film 204 may beremoved. Various films capable of preventing the doping of theimpurities of the second conductive type may be used as the capping film204. The capping film 204 may be removed by a removing method dependingon a material.

In the second conductive type semiconductor region forming step S5, foranother example, as shown in FIG. 15 , the second conductive typesemiconductor region 120 may be formed by forming a second doping layer310, including impurities of the second conductive type, on the frontsurface of the semiconductor substrate 100 and diffusing the impuritiesof the second conductive type, included in the second doping layer 310,into the semiconductor substrate 100 through thermal treatment.

The second doping layer 310 may include boron silicate glass (BSG) orphosphorous silicate glass (PSG). The second doping layer 310 may beeasily formed by deposition. In this instance, the second doping layer310 may be formed by atmospheric pressure chemical vapor deposition andmay not be formed on the back surface of the semiconductor substrate100.

Thereafter, as shown in FIG. 12 , the anti-reflection layer and secondpassivation film forming step S6 may be performed.

In the anti-reflection layer and second passivation film forming stepS6, the second passivation film 190B and the anti-reflection layer 130may be sequentially formed on the second conductive type semiconductorregion 120.

In the anti-reflection layer and second passivation film forming stepS6, for example, as shown in FIG. 13H, the second passivation film 190Band the anti-reflection layer 130 may be sequentially formed on the sideof the semiconductor substrate 100 in addition to the front surface ofthe second conductive type semiconductor region 120.

The second passivation film 190B or the anti-reflection layer 130 may beformed by various methods, such as a vacuum deposition method, achemical vapor deposition method, spin coating, screen printing, orspray coating.

If one-sided deposition, such as plasma-enhanced chemical vapordeposition (PECVD), is used when the second passivation film 190B or theanti-reflection layer 130 is formed, the second passivation film 190B orthe anti-reflection layer 130 may be formed on only the front surfaceand/or side of the semiconductor substrate 100. Accordingly, a separatepatterning process for the second passivation film 190B or theanti-reflection layer 130 is not required.

Thereafter, as shown in FIG. 12 , the first passivation film formingstep S7 for forming the first passivation film 190A on the firstconductive type semiconductor region 170 may be performed.

For example, as shown in FIG. 13I, the first passivation film 190A maybe formed on the first conductive type semiconductor region 170 placedon the back surface side of the semiconductor substrate 100, theisolation portion I placed in the edge of the back surface of thesemiconductor substrate 100, and the second passivation film 190B andthe anti-reflection layer 130 placed on the side of the semiconductorsubstrate 100.

Accordingly, after edge isolation according to the isolation portion Iis performed, the isolation portion I may also be passivated while thefirst passivation film 190A is formed without a separate process.

The first passivation film 190A may be formed by various methods, suchas a vacuum deposition method, a chemical vapor deposition method, spincoating, screen printing, or spray coating.

If one-sided deposition, such as plasma-enhanced chemical vapordeposition (PECVD), is used when the first passivation film 190A or theanti-reflection layer 130 is formed, the first passivation film 190A maybe formed on only the back surface and/or side of the semiconductorsubstrate 100. Accordingly, a separate patterning process for the firstpassivation film 190A is not required.

In the present embodiment, an example in which the second passivationfilm 190B covering the front surface side of the semiconductor substrate100 is first formed and the first passivation film 190A covering theback surface side of the semiconductor substrate 100 is then formed hasbeen described.

In this instance, the characteristics of the first conductive typesemiconductor region 170 can be prevented from being deteriorated ordamaged in the process of forming the first passivation film 190A. Thereason for this is that the characteristics of the first conductive typesemiconductor region 170 may be very important, in particular, if thefirst conductive type semiconductor region 170 is an emitter region.

However, the present invention is not limited to the example. Forexample, after the first passivation film 190A covering the back surfaceside of the semiconductor substrate 100 is formed, the secondpassivation film 190B covering the front surface side of thesemiconductor substrate 100 may be formed.

In this instance, the first passivation film 190A covering the backsurface side of the semiconductor substrate 100 may be placed on (e.g.,brought into contact with) the side of the semiconductor substrate 100,and the second passivation film 190B covering the front surface side ofthe semiconductor substrate 100 may be placed on (e.g., brought intocontact with) on the first passivation film 190A.

After the first passivation film 190A is formed as described above, asshown in FIGS. 12 and 13J, the electrode forming step S8 for forming thefirst electrode 150 connected to the first conductive type semiconductorregion 170 and the second electrode 140 connected to the secondconductive type semiconductor region 120 may be performed.

The electrode forming step S8 may include the step (operation) offorming the opening portion 102 in the first passivation film 190A.Accordingly, in the electrode forming step S8, the first and the secondopening portions 102 and 104 may be formed in the first and the secondpassivation films 190A and 190B by a patterning process, for example.Next, the first and the second electrodes 150 and 140 may be formedwhile the first and the second opening portions 102 and 104 are filledwith metal for forming the first and the second electrodes 150 and 140.

In this instance, the first and the second opening portions 102 and 104may be formed by laser ablation using a laser or various methods usingan etch solution, an etch paste, and a photo process. Furthermore, thefirst and the second electrodes 150 and 140 may be formed by variousmethods, such as a plating method or a deposition method.

Accordingly, the isolation portion I can be formed by a simple process,and a problem attributable to surface recombination can be prevented bypassivating the isolation portion I using the first passivation film190A. Accordingly, productivity can be improved because a defectiveratio of solar cells is reduced through a simple process.

In some embodiments, in the electrode forming step S8, the first and thesecond electrodes 150 and 140 may be formed by coating pastes forforming the first and the second electrodes 150 and 140 on the first andthe second passivation films 190A and 190B using screen printing andthen using a thermal treatment method, such as fire through or laserfiring contact (or laser firing contact).

If the first electrode and the second electrode are formed using aprinting method and a thermal treatment method as described above, thefirst and the second opening portions 102 and 104 are naturally formedwhen the first and the second electrodes 150 and 140 are formed.Accordingly, the manufacturing process can be further simplified becausea separate process for forming the first and the second opening portions102 and 104 is not required.

An example in which the first electrode and the second electrode areformed using a printing method and a thermal treatment method asdescribed above is described in more detail below.

FIG. 16 is a flowchart illustrating an example of a method formanufacturing a solar cell according to a second embodiment of thepresent invention. FIG. 17 is a flowchart illustrating an example of amethod for manufacturing a solar cell according to a third embodiment ofthe present invention.

The remaining steps (operations) of FIGS. 16 and 17 other than a firstelectrode forming step are the same as those of FIGS. 12 and 13A to 15 ,and thus different portions are chiefly described.

Accordingly, as in the manufacturing method of the first embodiment,each of the methods for manufacturing a solar cell according to thesecond embodiment and third embodiment of the present invention mayinclude the tunnel layer forming step S1, the intrinsic semiconductorlayer forming step S2, the first conductive type semiconductor regionforming step S3, the removing step S4, the second conductive typesemiconductor region forming step S5, the anti-reflection layer andsecond passivation film forming step S6, the first passivation filmforming step S7, and the electrode forming step S8.

The remaining steps (operations) other than the electrode forming stepS8 may be the same as those of the first embodiment, and thus adescription thereof is omitted.

In the second embodiment or the third embodiment, the electrode formingstep S8 may include the step of forming the first electrode and the stepof forming the second electrode. In this instance, the step of formingthe second electrode may be the same as that of the method formanufacturing a solar cell according to the first embodiment of thepresent invention, or the first electrode forming step S8 according tothe second embodiment or the third embodiment may be applied to the stepof forming the second electrode without a change. Accordingly, in anembodiment of the present invention, a detailed description of themethod for forming the second electrode is omitted because it is notspecially limited.

The step of forming the first electrode in the second embodiment or thethird embodiment is described in detail because it is different fromthat in the first embodiment.

In the method for manufacturing a solar cell according to the secondembodiment or the third embodiment, the first electrode forming step S8may include a process for printing a paste for the first fingerelectrodes for forming the first finger electrodes and a paste for thefirst bus bar for forming the first bus bar on the first passivationfilm 190A and a thermal treatment process.

In the thermal treatment process, the paste for the first fingerelectrodes and the paste for the first bus bar may perforate the firstpassivation film and may be connected to the first conductive typesemiconductor region. Accordingly, the step of forming the openingportion in the first passivation film may be performed during thethermal treatment process of the electrode forming step.

More specifically, in the method for manufacturing a solar cellaccording to the second embodiment of the present invention, a firstelectrode forming step S8A may include a process S8A1 for printing thepaste for the first finger electrodes and the paste for the first busbar on the first passivation film 190A through a single printing processand a thermal treatment process S8A2.

In this instance, a material included in the paste for the first fingerelectrodes for forming the first finger electrodes 151 and a materialincluded in the paste for the first bus bar for forming the first busbar 153 may be the same.

Thereafter, the paste for the first finger electrodes and the paste forthe first bus bar perforate the first passivation film 190A and areconnected to the first conductive type semiconductor region 170 throughthe thermal treatment process. Accordingly, the paste for the firstfinger electrodes and the paste for the first bus bar may be partiallydepressed into the first conductive type semiconductor region 170 andthen fired, thereby forming the first finger electrodes 151 and thefirst bus bar 153, such as those shown in FIG. 5 .

Furthermore, during the thermal treatment process, metal may beextracted from the paste for the first finger electrodes and the pastefor the first bus bar and recrystallized. Accordingly, the metalcrystals MC may be formed in the electrode forming region 170A of thefirst conductive type semiconductor region 170.

In this instance, the highest temperature of the thermal treatmentprocess may be between 700° C. to 900° C., more specifically, between795° C. to 870° C.

If the highest temperature of the thermal treatment process is 795° C.or more, the paste for the first finger electrodes and the paste for thefirst bus bar can perforate the first passivation film 190A and can beconnected to the first conductive type semiconductor region 170.

If the highest temperature of the thermal treatment process is 870° C.or less, the metal crystals MC recrystallized when metal is extractedfrom the paste for the first finger electrodes and the paste for thefirst bus bar can be prevented from penetrating the tunnel layer 160.

Furthermore, in the method for forming a solar cell according to thethird embodiment of the present invention, a first electrode formingstep S8B may include a process S8B1 for printing the paste for the firstfinger electrodes on the first passivation film 190A in order to formthe first finger electrodes 151, a process S8B2 for printing the pastefor the first bus bar having a material different from the material ofthe paste for the first finger electrodes on the first passivation film190A in order to form the first bus bar 153, and a thermal treatmentprocess S8B3, as shown in FIG. 17 .

In FIG. 17 , the process S8B1 for printing the paste for the firstfinger electrodes has been illustrated as being first performed and theprocess S8B2 for printing the paste for the first bus bar has beenillustrated as being then performed, but sequence of the two processesmay be reversed.

As described above, the first finger electrodes 151 and the first busbar 153, such as those shown in FIG. 9 , may be formed through the firstelectrode forming step S8, such as that shown in FIG. 17 .

As described above, in the method for forming a solar cell according tothe third embodiment of the present invention, the paste for the firstfinger electrodes and the paste for the first bus bar may be performedby the separate printing processes S8B1 and S8B12.

Furthermore, in this instance, a material included in the paste for thefirst finger electrodes and a material included in the paste for thefirst bus bar may be different.

More specifically, content of frit glass per unit volume which isincluded in the paste for the first bus bar may be smaller than contentof frit glass per unit volume which is included in the paste for thefirst finger electrodes, or frit glass may not be included in the pastefor the first bus bar.

The reason for this is that while the paste for the second fingerelectrodes perforates the first passivation film 190A and is depressedinto the first conductive type semiconductor region 170 in the thermaltreatment process for forming the first electrode 150, the paste for thefirst bus bar perforates the first passivation film 190A, but is rarelydepressed into the first conductive type semiconductor region 170although it is connected to the first conductive type semiconductorregion 170 or the paste for the first bus bar does not perforate thefirst passivation film 190A.

In this instance, the metal crystals MC may not be formed in the bus barforming region 170A2 of the first conductive type semiconductor region170, and the semiconductor substrate 100 can be prevented from beingdeteriorated.

Furthermore, content of frit glass per unit volume which is included inthe plurality of first finger electrodes 151 may be the same as contentof frit glass per unit volume which is included in the second electrode140.

After the paste for the second electrode is coated, the second electrode140 may also perforate the anti-reflection layer 130 and may beconnected to the second conductive type semiconductor region 120. Ifcontent of frit glass per unit volume which is included in the paste forthe second finger electrodes is the same as that included in the secondelectrode 140, speed at which the paste for the second electrodeperforates the anti-reflection layer 130 and is depressed into thesecond conductive type semiconductor region 120 and speed at which thepaste for the second finger electrodes perforates the first passivationfilm 190A and is depressed into the first conductive type semiconductorregion 170 in the same thermal treatment process may becomeapproximately the same.

Accordingly, temperatures in the thermal treatment processes for formingthe second electrode 140 and the first electrode 150 may become thesame, and speed at which the first finger electrodes 151 are depressedinto the first conductive type semiconductor region 170 can be limited.

Furthermore, content of a metal material per unit volume which isincluded in the plurality of first finger electrodes 151 may be greaterthan content of a metal material per unit volume which is included inthe plurality of first bus bars 153.

For example, content of a metal material per unit volume which isincluded in the plurality of first finger electrodes 151 may be 80 wt %or more to 95 wt % or less. Content of a metal material per unit volumewhich is included in the plurality of first bus bars 153 may be 60 wt %or more 80 wt % or less.

If content of a metal material per unit volume which is included in thefirst finger electrodes 151 is 80 wt % or more 95 wt % or less asdescribed above, the metal crystals MC can be sufficiently formed asdescribed above with reference to FIG. 6 and resistance of the firstfinger electrodes 151 having relatively narrow widths can besufficiently lowered in the state in which the paste for the secondfinger electrodes has perforated the first passivation film 190A and isdepressed into the first conductive type semiconductor region 170.

Furthermore, if content of a metal material per unit volume which isincluded in the first bus bar 153 is 60 wt % or more 80 wt % or less,the metal crystals MC may not be formed in the bus bar forming region170A2 of the first conductive type semiconductor region 170 due to themetal material included in the paste for the first bus bars althoughpart of the paste for the first bus bars perforates the firstpassivation film 190A and is connected to the first conductive typesemiconductor region 170, or the metal crystals MC may not be formed inthe tunnel layer 160 as described above with reference to FIG. 7although the metal crystals MC are formed in the bus bar forming region170A2.

Furthermore, content of a metal material per unit volume which isincluded in the plurality of first finger electrodes 151 may be the sameas content of a metal material per unit volume which is included in thesecond electrode 140.

If the first finger electrodes 151 and the first bus bar 153 havingdifferent materials are formed as described above, the deterioration ofthe semiconductor substrate 100 can be prevented, and the deteriorationof efficiency of the solar cell can be further prevented.

As described above, the deterioration of the semiconductor substrate 100may be generated during the thermal treatment process for forming thefirst electrode 150. If a temperature in the thermal treatment processis too low, the deterioration of efficiency of the solar cell can beprevented because contact resistance of the first electrode 150 isexcessively increased.

The embodiments of the present invention have been described in detailabove, but the scope of the present invention is not limited thereto.The scope of the present invention also includes a variety ofmodifications and changes which are defined in the appended claims andwhich will be performed by those skilled in the art using the basicconcept of the present invention.

What is claimed is:
 1. A solar cell, comprising: a single-crystalsilicon semiconductor substrate; a polysilicon back surface field layerformed on a first surface of the single-crystal silicon semiconductorsubstrate; an oxide layer disposed between the single-crystal siliconsemiconductor substrate and the polysilicon back surface field layer; anemitter region formed at a second surface of the single-crystal siliconsemiconductor substrate; a dielectric film covering the polysilicon backsurface field layer; a first electrode connected to the polysilicon backsurface field layer through the dielectric film; a passivation film onthe emitter region; and a second electrode connected to the emitterregion through the passivation film, wherein a contact area in which thefirst electrode is connected to the polysilicon back surface fieldlayer, includes a plurality of metal crystals extracted from the firstelectrode, wherein a height difference between a first interface, whichis an interface between the first electrode and the polysilicon backsurface field layer, and a second interface, which is an interfacebetween the polysilicon back surface field layer and the dielectricfilm, is 1 nm-20 nm, wherein the plurality of metal crystals are mostlyformed at the polysilicon back surface field layer and are not extendedto the oxide layer and the single-crystal silicon semiconductorsubstrate in order to prevent damage of the oxide layer or thesingle-crystal silicon semiconductor substrate, wherein the firstelectrode includes a plurality of first finger electrodes extending in afirst direction and a first bus bar extending in a second directioncrossing the first direction, and wherein an amount of glass frit perunit volume in the plurality of first finger electrodes is less than anamount of glass frit per unit volume in the first bus bar.
 2. The solarcell of claim 1, wherein the second electrode comprises a plurality ofsecond finger electrodes spaced apart from each other and extended inparallel in the first direction.
 3. The solar cell of claim 2, whereinthe second electrode further comprises a second bus bar connected to theplurality of second finger electrodes.
 4. The solar cell of claim 1,further comprising an isolation portion for preventing a contact betweenthe polysilicon back surface field layer and the emitter region, whereinthe isolation portion is formed on at least one of the first surface ofthe single-crystal silicon semiconductor substrate, a side surface ofthe single-crystal silicon semiconductor substrate, or the secondsurface of the single-crystal silicon semiconductor substrate.
 5. Thesolar cell of claim 4, wherein the isolation portion excludes the oxidelayer and the polysilicon back surface field layer, and is in an edgeportion of the first surface of the single-crystal silicon semiconductorsubstrate, and wherein the dielectric film covers the first surface ofthe single-crystal silicon semiconductor substrate and the isolationportion together.
 6. The solar cell of claim 4, wherein a width of theisolation portion is 1 nm to 1 mm.
 7. The solar cell of claim 4, whereina thickness of an edge region in the polysilicon back surface fieldlayer progressively decreases toward the isolation portion.
 8. The solarcell of claim 1, wherein the dielectric film comprises a side portionextending up a side surface of the single-crystal silicon semiconductorsubstrate.
 9. The solar cell of claim 8, wherein the passivation filmcomprises a side portion formed on the side surface of thesingle-crystal silicon semiconductor substrate, and wherein the sideportion of the dielectric film on the side surface of the single-crystalsilicon semiconductor substrate is on the side portion of thepassivation film.
 10. The solar cell of claim 1, wherein the secondsurface of the single-crystal silicon semiconductor substrate is a lightincident surface, the first surface of the single-crystal siliconsemiconductor substrate is a back surface of the single-crystal siliconsemiconductor substrate.
 11. The solar cell of claim 3, wherein all ofthe plurality of first finger electrodes and the first bus bar areconnected to the polysilicon back surface field layer through thedielectric film.
 12. The solar cell of claim 11, wherein all of theplurality of first finger electrodes and the first bus bar have a singlelayer structure or a double layer structure.
 13. The solar cell of claim11, wherein the plurality of first finger electrodes have a single layerstructure, and wherein the first bus bar has a double layer structure.14. The solar cell of claim 1, wherein the dielectric film and thepassivation film are formed of a plurality of layers.
 15. The solar cellof claim 1, wherein a thickness of the polysilicon back surface fieldlayer is greater than a thickness of the dielectric film.
 16. The solarcell of claim 1, wherein the plurality of metal crystals include firstmetal crystals which directly contact with the first electrode, andsecond crystals which are spaced apart from the first electrode andformed in the polysilicon back surface field layer.